diff --git a/qa/rpc-tests/bip68-sequence.py b/qa/rpc-tests/bip68-sequence.py
--- a/qa/rpc-tests/bip68-sequence.py
+++ b/qa/rpc-tests/bip68-sequence.py
@@ -32,9 +32,9 @@
     def setup_network(self):
         self.nodes = []
         self.nodes.append(
-            start_node(0, self.options.tmpdir, ["-blockprioritysize=0"]))
+            start_node(0, self.options.tmpdir, ["-blockprioritypercentage=0"]))
         self.nodes.append(
-            start_node(1, self.options.tmpdir, ["-blockprioritysize=0",
+            start_node(1, self.options.tmpdir, ["-blockprioritypercentage=0",
                                                 "-acceptnonstdtxn=0"]))
         self.is_network_split = False
         self.relayfee = self.nodes[0].getnetworkinfo()["relayfee"]
diff --git a/qa/rpc-tests/smartfees.py b/qa/rpc-tests/smartfees.py
--- a/qa/rpc-tests/smartfees.py
+++ b/qa/rpc-tests/smartfees.py
@@ -214,14 +214,14 @@
         # NOTE: the CreateNewBlock code starts counting block size at 1,000 bytes,
         # (17k is room enough for 110 or so transactions)
         self.nodes.append(start_node(1, self.options.tmpdir,
-                                     ["-blockprioritysize=1500", "-blockmaxsize=17000",
+                                     ["-blockprioritypercentage=9", "-blockmaxsize=17000",
                                       "-maxorphantx=1000"],
                                      stderr_checker=OutputChecker()))
         connect_nodes(self.nodes[1], 0)
 
         # Node2 is a stingy miner, that
         # produces too small blocks (room for only 55 or so transactions)
-        node2args = ["-blockprioritysize=0",
+        node2args = ["-blockprioritypercentage=0",
                      "-blockmaxsize=8000", "-maxorphantx=1000"]
 
         self.nodes.append(
@@ -294,5 +294,6 @@
         self.log.info("Final estimates after emptying mempools")
         check_estimates(self.nodes[1], self.fees_per_kb, 2)
 
+
 if __name__ == '__main__':
     EstimateFeeTest().main()
diff --git a/src/init.cpp b/src/init.cpp
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -784,11 +784,11 @@
         "-blockmaxsize=<n>",
         strprintf(_("Set maximum block size in bytes (default: %d)"),
                   DEFAULT_MAX_GENERATED_BLOCK_SIZE));
-    strUsage +=
-        HelpMessageOpt("-blockprioritysize=<n>",
-                       strprintf(_("Set maximum size of high-priority/low-fee "
-                                   "transactions in bytes (default: %d)"),
-                                 DEFAULT_BLOCK_PRIORITY_SIZE));
+    strUsage += HelpMessageOpt(
+        "-blockprioritypercentage=<n>",
+        strprintf(_("Set maximum percentage in size of high-priority/low-fee "
+                    "transactions in bytes (default: %d)"),
+                  DEFAULT_BLOCK_PRIORITY_PERCENTAGE));
     strUsage += HelpMessageOpt(
         "-blockmintxfee=<amt>",
         strprintf(_("Set lowest fee rate (in %s/kB) for transactions to be "
diff --git a/src/miner.cpp b/src/miner.cpp
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -561,13 +561,20 @@
 void BlockAssembler::addPriorityTxs() {
     // How much of the block should be dedicated to high-priority transactions,
     // included regardless of the fees they pay.
-    uint64_t nBlockPrioritySize =
-        GetArg("-blockprioritysize", DEFAULT_BLOCK_PRIORITY_SIZE);
-    nBlockPrioritySize = std::min(nMaxGeneratedBlockSize, nBlockPrioritySize);
-    if (nBlockPrioritySize == 0) {
+    uint8_t nBlockPriorityPercentage =
+        GetArg("-blockprioritypercentage", DEFAULT_BLOCK_PRIORITY_PERCENTAGE);
+    if (nBlockPriorityPercentage == 0) {
         return;
     }
 
+    // nBlockPriorityPercentage needs to belong to [0..100] interval
+    nBlockPriorityPercentage =
+        std::min(static_cast<uint8_t>(100), nBlockPriorityPercentage);
+    nBlockPriorityPercentage =
+        std::max(static_cast<uint8_t>(0), nBlockPriorityPercentage);
+    uint64_t nBlockPrioritySize =
+        nMaxGeneratedBlockSize * nBlockPriorityPercentage / 100;
+
     // This vector will be sorted into a priority queue:
     std::vector<TxCoinAgePriority> vecPriority;
     TxCoinAgePriorityCompare pricomparer;
@@ -590,7 +597,8 @@
 
     CTxMemPool::txiter iter;
 
-    // Add a tx from priority queue to fill the blockprioritysize.
+    // Add a tx from priority queue to fill the part of block reserved to
+    // priority transactions.
     while (!vecPriority.empty() && !blockFinished) {
         iter = vecPriority.front().second;
         actualPriority = vecPriority.front().first;
diff --git a/src/policy/policy.h b/src/policy/policy.h
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -17,9 +17,10 @@
 /** Default for -blockmaxsize, which controls the maximum size of block the
  * mining code will create **/
 static const uint64_t DEFAULT_MAX_GENERATED_BLOCK_SIZE = 2 * ONE_MEGABYTE;
-/** Default for -blockprioritysize, maximum space for zero/low-fee transactions
+/** Default for -blockprioritypercentage, maximum percentage space for
+ * zero/low-fee transactions
  * **/
-static const uint64_t DEFAULT_BLOCK_PRIORITY_SIZE = 0;
+static const uint64_t DEFAULT_BLOCK_PRIORITY_PERCENTAGE = 5;
 /** Default for -blockmintxfee, which sets the minimum feerate for a transaction
  * in blocks created by mining code **/
 static const unsigned int DEFAULT_BLOCK_MIN_TX_FEE = 1000;
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -78,7 +78,7 @@
 // Test suite for ancestor feerate transaction selection.
 // Implemented as an additional function, rather than a separate test case, to
 // allow reusing the blockchain created in CreateNewBlock_validity.
-// Note that this test assumes blockprioritysize is 0.
+// Note that this test assumes blockprioritypercentage is 0.
 void TestPackageSelection(const CChainParams &chainparams, CScript scriptPubKey,
                           std::vector<CTransactionRef> &txFirst) {
     // Test the ancestor feerate transaction selection.
@@ -86,6 +86,9 @@
 
     GlobalConfig config;
 
+    // these 3 tests assume blockprioritypercentage is 0.
+    ForceSetArg("-blockprioritypercentage", "0");
+
     // Test that a medium fee transaction will be selected after a higher fee
     // rate package with a low fee rate parent.
     CMutableTransaction tx;