Abstract: In order to analyze the mechanical properties of laser transmission welding of polycarbonate,the transparent and opaque polycarbonates were welded by a 10 W diode end pumped solid state laser,respectively.The microstructure,fracture appearance, micro-hardness and tensile-shear strength of the welded joint were tested by optical metallographic microscope (OM),field emission scanning electron microscope (SEM), micro-hardness tester and electronic universal tensile machine, respectively.The results showed that the joint gradually become as similar adhesive joint from welded joint with the increase of laser power density.Layering and pores in the welded joint are the defects to resulting in poor mechanical properties.The mechanical properties of the welded joint can be improved by controlling laser power density.At the laser power density of 0.23 J/mm², the tensile-shear stresses reaches 44 MPa,which is 68% of that of the basic materials.The micro-hardness on the center of the welded joint is very close to the basic material.The fracture is the mixture of ductile fracture and brittle fracture.