In this study, laser transmission welding of two heterogeneous polymeric materials was performed and the effect of laser process parameters on the weld joint strength was investigated by shear test corresponding to ASTM standard D3163-01. Specifically, laser transmission welding of 2 ㎜ thick PMMA and PC/ABS was performed using a thulium laser with wavelength and focusing diameter of 2 ㎛ and 1 ㎜, respectively. The experimental results showed that the bonding strength increases as the laser energy transmitted to the welding zone increases, but too strong energy causes a decrease in the mechanical properties of the heat-affected zone. Thus, it is necessary to find the laser process parameters (Maximum Laser Power and Laser Scan Speed) that can secure sufficient bonding strength within the allowable range where surface defects do not occur in the actual process.