Laser transmission welding properties between two dissimilar polymers- polycarbonate and polyphenylene oxide are studied. The influence of temperature properties and compatibility on the weld ability are investigated. Diode laser and tensile machine are used for the welding and tensile-shear test respectively. The process parameters are designed and optimized through response surface methodology. Failure forms of weld joint under different scanning velocities are investigated by observing the fracture morphology through a 3D microscope. The results show that under the condition of 6.34 W power, 40 mm/s scanning velocity, 0.39 MPa clamp pressure, the best tensile-shear strength is 6.51 MPa. The compatibility between two melting polymers and the welding defects (ablation and voids) are the major factors that determine the mechanical properties and failure form of the joints. Dissimilar polymers are weldable by laser transmission welding.