To decrease the laser welding defects of 6061 aluminum alloy lap joints, laser wobble welding was employed, and the effect of the laser beam wobble on the weld formation, microstructure and microhardness was studied. Results show that the weld formation is instability, and a large number of porosities exist in the center of the weld for the lap joints without laser wobble. By using the laser wobble welding, the weld formation is improved, and the porosities are decreased. When the wobble amplitude and frequency are set as 1.0-1.5 mm and 100-300 Hz, respectively, the weld formation is good, and the porosity is less than 0.6%. Compared to the lap joints without wobble welding, the weld shape of wobble weld joints is changed from Y-shaped to U-shaped, and the grain refinement occurs. The size of columnar crystal is reduced from 380 μm to 130 μm, and the size of equiaxed crystal is decreased from 120 μm to 75 μm. Micro hardness is increased from 60 HV to 65 HV by using laser wobble welding.