Analysis of the thermal effect and machining properties of PC (polycarbonate) and ABS (polyacrylonitrilebutadienestyrene) polymers when ablated using a KrF excimer laser is described. PC has less thermal effect on the geometric distortion than ABS in laser ablation. The cumulative heat during laser ablation results in geometric deformation in ABS micromachining. The number of laser pulses generates a greater geometric deformation in ABS than in PC according to experimental laser ablation observations. The PC ablation rate is proportional to the laser fluence, whereas ABS shows an exponential profile. The pulse repetition rate has no significant influence on PC during laser ablation, but affects the ablated patterns in ABS. During laser ablation, PC does not produce debris on the machining patterns, but debris is produced on the machining patterns with ABS.