The research was study the effect of gas metal arc welding process parameters on mechanical property. The specimen was carbon steel ASTM A285 grade A which thickness of 6 mm. The experiments with full factorial design. The factors used in this study are shielding gas and voltage. The welded specimens were tested by tensile strength testing and hardness testing according to ASME boiler and pressure vessel code section IX 2007. The result showed that both of shielding gas and voltage had interaction on tensile strength and hardness at 95% confidential (P value < 0.05). Factors affecting the tensile strength are the most carbon dioxide and 27 voltage were tensile strength 213.43 MPa. And hardness maximum of 170.60 HV can be used carbon dioxide and 24 voltage. This research can be used as data in the following appropriate parameters to gas metal arc welding process.