In the present work through transmission laser welding (TTLW) of two transparent plastic materials namely, Acrylic and Polycarbonate at varied levels of laser power, scanning speed and frequency have been carried out to form lap joints without application of filler material. The effect of input parameters on the weld quality has been studied through inspection and tests. Statistical software Design Expert 10 has been applied for design of experiments and analysis purpose. Breaking load and weld width have been considered as responses. Response surface methodology (RSM) has been applied for multi-objective optimization for minimization of weld width and maximization of breaking load simultaneously. Confirmatory tests have been conducted to validate the applied optimization techniques.