During dissimilar friction stir welding (FSW) of Al-Mg2Si metal matrix composite and AA6061 aluminum alloy, the temperature field and heat generation were investigated using a 3-dimensional computational fluid dynamics (CFD) model and FLUENT software. The simulations were conducted for rotational speeds of 720, 920 and 1120 rpm. The welding experiments were carried out to validate the simulation results. About 70 per cent of the heat generates at the interface between the shoulder and the workpiece. The maximum temperature was predicted on the advancing side (AS). The difference between the peak temperatures on the AS and the retreating side (RS) was about 115 K. The effect of the rotational speed on the peak temperature is significant. The temperature distribution in the cross-sections is asymmetric, which originates from different material velocities on the AS and RS. The peak temperature on the RS develops under the top surface, while the peak temperature on the AS develops on the surface.