Due to the environmental problem, automotive companies are trying to reduce the weight of the car body. Therefore, TRIP (TRansformation Induced Plasticity) steels, which have high strength and ductility, have been developed. However, there are only a few publication reported on the characteristics of GMA weld on TRIP steel. In this study, we will evaluate which of the shielding gases, i.e. Ar 100% CO2 100% and Ar 85% + CO2 15%, and welding speed make a better quality GMA welded TRIP steel. Bead-on plate welding and butt welding were performed with various welding conditions. In order to identify mechanical properties of welded TRIP steel experimental methods including fractography, tensile test, and hardness test were performed.