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.