The　combustion　process　within　the　cylinder　directly　influences　the　thermal　efficiency　and　performance　of　the　engines.　As　for　the　rotary　engine,　the　long-narrow　combustion　chamber　prevents　the　mixture　from　fully　burning,　which　worsens　the　performance　of　the　rotary　engine.　As　a　fuel　with　excellent　properties,　hydrogen　can　improve　the　combustion　of　the　original　engine.　In　this　paper,　improvements　in　combustion　of　a　gasoline　rotary　engine　by　hydrogen　supplement　under　different　operating　conditions　were　experimentally　investigated.　The　experiment　was　conducted　on　a　modified　hydrogen-gasoline　dual-fuel　rotary　engine　equipped　with　an　electronically-controlled　fuel　injection　system.　An　electronic　control　module　was　specially　made　to　command　the　fuel　injection,　excess　air　ratio　and　hydrogen　volumetric　fraction.　Integral　heat　release　fraction　(IHRF)　was　employed　to　evaluate　the　combustion　of　the　tested　engine.　The　tested　engine　was　first　run　at　the　idle　speed　of　2400　rpm　and　then　operated　at　4500　rpm　to　investigate　the　combustion　of　the　hydrogen-blended　gasoline　rotary　engine　under　different　hydrogen　volume　fractions,　excess　air　ratios　and　spark　timings.　The　testing　results　demonstrated　that　the　combustion　of　the　gasoline　rotary　engine　were　all　improved　when　the　hydrogen　was　blended　into　the　chamber　under　all　tested　conditions.　(C)　2017　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.