In this study, investigations on the hydrogen usage in spark ignition (SI) rotary engines are reviewed to assess trend researches. Many scientists conducted various studies to investigate performance, emission and combustion characteristics of hydrogen technology. The studies generally focused on their usage as an additive fuel. It can be seen that hydrogen usage in SI engine are very promising for their lower emissions, more efficient combustion, and higher power output. Nevertheless, hydrogen utilization may cause combustion problems such as back fire, auto and pre-ignition. Moreover, because of their small molecular structure hydrogen storage is another issue. Especially, hydrogen blending is a particular solution and this makes hydrogen gas tolerable for storage and transporting problem. In the recent studies, hydrogen usage in rotary engine is found well suited and feasible by scientists. Combustion difficulties caused by long and narrow shaped combustion chamber and long quenching distance of this type of engine can be solved by hydrogen addition. However, absence of a light, safe and low cost storage technology are still bottlenecks for their usage and waiting for solution. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.