The problem of the slow migration of a bubble in non-Newtonian fluids in the presence of a thermal gradient is solved by the method of perturbation. We have considered separately a fluid with constant viscosity which exhibits normal stress differences in viscometric flow and a fluid with variable viscosity. We have made a qualitative analysis and shown that in a non-Newtonian fluid the shape of the bubble might not be spherical. We have calculated the terminal velocity and found that for small bubbles the effects of a surface tension gradient is dominant whereas for large bubbles the surface tension gradient can be neglected.