The effects of rotation on the stability and structure of tubular flames have been investigated for a lean hydrogen/air mixture, and mechanism of flame stability in a rotating flow has been discussed. Results show that with increasing intensity of rotation, (1) the flame diameter increases, while thickness of the luminous zone decreases, (2) the fuel concentration at the extinction decreanes, i. e., the stable region expands, (3) the radial temperature distribution becomes an M-shaped profiles, and (4) flame temperature T_f increases near extinction. These results are almost the same as those obtained for a methane/air mixture. The mechanism for these phenomena is supposed to be explained with the coupled effects of pressure diffusion and stretch effect. The present experimental results provide very useful information for discussing the flame stability and the transport phenomena in a vortex flow.