Under microgravity environments, the thermocapillary migration of a deformable gas bubble placed in a liquid with a constant temperature gradient is investigated numerically. A finite difference method with boundary- fitted coordinates is employed to solve the axisymmetric governing equations. An iterative procedure is introduced for the computation of the deformable shape and the thermal velocity of the gas bubble. The influence of the Marangoni and capillary numbers is considered. Results of the computations show that the terminal velocity of the gas bubble is reduced significantly by the effect of surface deformation.