The polymer melts viscous dissipation effects of micro scale dimensions are different from that of macro-scale dimensions. In this paper, the temperature rises due to viscous dissipation were investigated when amorphous polymer material, PMMA, flows through several micro-channels with the diameters of 350μm, 500μm and different aspect ratios. The results indicate that, temperature rises reduce with the increase of inlet temperature of melt and increase with increasing channel’s diameter and aspect ratio at the same shear rate. The outlet temperature rises due to viscous dissipation in all micro channels increase with the increase of shear rate. In addition, the outlet temperature rise grows faster with the decrease of micro-channel’s diameter. Therefore, viscous dissipation effect is significant and should not be neglected in micro channel.