The present study investigates the thermal-diffusion and diffusion-thermo effects of a viscous fluid in a two-dimensional channel between slowly expanding or contracting walls with weak permeability. Assuming symmetric injection or suction along the uniformly expanding porous walls and using similarity transformation, the governing flow equations are reduced to nonlinear ordinary differential equations. The resulting equations are then solved analytically using a perturbation technique in permeation Reynolds number and wall dilation ratio. The effects of various physical parameters on flow variables have been discussed numerically and explained graphically.