In the automotive industry, the use of thermoplastic and laser transmission source in vehicle lighting systems stands out because of the superior properties, and it is widely used in production and joining processes. However, as the process parameters directly affect the welding quality, it is very important to determine their effects. In this study, 2,7 mm thick Acrylonitrile butadiene styrene (ABS) and transparent Polymethyl methacrylate (PMMA) materials are combined with LPKF Twinweld 3D 6000 laser device. The effects of laser power, pressure force and feed rate, which are important parameters in laser transmission welding, are investigated. Lab-joint welding is performed with ABS and PMMA materials at 20-50 W laser power, 30-150 mm /s laser speed and 55-85 N pressure force. Samples combined in different parameter combinations are subjected to tensile tests, their mechanical strengths are examined and correlate with the parameters. As a result of the tests, the highest average mechanical strength and average elongation at break are obtained in the combination of 30 W, 70 mm/s and 70 N parameters. When all other parameters are kept constant, it is seen that the most effective parameter on mechanical strength is laser power.