In this work, a fractional order (FO) proportional–integral–derivative (PID) (FO-PID) controller is considered for load-frequency control (LFC) of the isolated hybrid power system, comprising of a biomass-based diesel engine generator and a wind turbine generator. The FO-PID controllers are PID controller only, and the difference lies in the order of the integral and derivative part of the controllers. In FO controllers, the order of the integral and derivative part are fractional in nature. In this paper, particle swarm optimization (PSO) algorithm has been engaged to carry out the above mentioned LFC for the considered wind-biomass isolated hybrid power system. A comparison of FO control strategy with conventional based controller techniques is made. The FO-PID controller outperforms the conventional PID controllers. And, robustness analysis is also done for the FO-PID controller.