The aim of this paper is to use the thermo-viscous expansion-contraction effect to enhance mixing in micro channels. To do this, numerical simulation of chaos flow generated by periodic thermal boundary condition in a 2-D microchannel is considered. The main objectives are to evaluate the effect of Reynolds number, Strouhal number and thermal penetration length on chaotic mixing. The vorticity is used as a criteria evaluating the chaos. It is shown that thermo-viscous expansion-contraction effect can be used as aconsiderable potential mean for micro-scale chaotic mixingpotential mean for micro-scale chaotic mixing. The results show that, the vorticity generated by change of density and viscosity due to the temperature difference caused by periodic heat transfer at flow boundary is mainly a function of dimensionless flow velocity and film thickness.