Micro weld lines are the common problem that occurs for plastic molded parts through injection molding process. This study focus on the formation of weld lines of molten polypropylene and polypropylene-glass-fiber reinforced composite under different parameters (melt temperature, material & mold design). Three different mold with different design were fabricated and injected with molten polypropylene and polypropylene-glass-fiber reinforced. The experimental result of the length, angle and location of the weld line were compared to the result from Autodesk Simulation Moldflow Adviser software. The result show a good resemblance with polypropylene with melt temperature 240oC and polypropylene-glass-fiber reinforced (10, 20, 25%) but not with polypropylene with melt temperature 250oC and 260oC. It is also concluded that the melt temperature, type of material and mold design affects the formation of weld lines.