Abstract: The 1.2 mm 2A12 was friction stir lap welded with 4.0 mm 7A09 aluminum alloys in different welding parameters. Specimen were subjected to tensile testing and observed by metallographic. The results showed that tensile force of joint was higher when the thick plate up to the sheet one. The maximum tensile strength of 17 kN, account for 85% of parent metal, as rotation and welding speed set as 800 and 400 mm/min. Tensile force was increasing with reduce of interface boundary in intersecting surface of joint. All the fractures were appeared at the beginning of weld joint on sheet plate, showing mixed fracture.