This paper discusses results obtained in a study of the transition to turbulence of gas jet diffusion flames in microgravity. The experiments were conducted at the 2.2-second Drop Tower of the NASA Lewis Research Center. Propane flames burning in quiescent air at atmospheric pressure were investigated. Significant differences have been observed between the transition processes of gas jet diffusion flames in microgravity and normal gravity These include the appearance of large scale structures in microgravity which are manifested at the flame base and are convected downstream. These structures appear intermittently at first, and, then, as Reynolds number is increased, a continuous train of structures is observed along the flame front. The experimental observations are explained in terms of flow transition and instability of the shear layer associated with the injection of the jet flow into quiescent surroundings