The GEN 125 is a Japanese aircraft engine, designed and produced by the GEN Corporation for use in ultralight helicopters.
The engine is a twin cylinder two-stroke, horizontally-opposed, air-cooled, , direct-drive, gasoline engine design. It employs capacitor discharge ignition and produces at 8500 rpm. The engine weighs .
The engine was designed specifically for the GEN H-4 helicopter, in which four of the engines are mounted to provide redundancy.