Mechanical properties of friction stir welded (FSWed), double sided arc welded (DSAWed), fiber laser welded (FLWed) and diode laser welded (DLWed) on AZ31B Mg alloy were studied. After welding, grains at the centre became recrystallized. Brittle phase β-Mg₁₇AI₁₂ particles observed at the centre of the joint during fusion welding process. The yield strength (YS), ultimate tensile strength (UTS) and fatigue strength were lower in the FDWed samples than in the DSAWed samples. Welding defect at the bottom of the FDWed joint was observed when right hand thread (RHT) weld tool was considered. In FLWed joint, YS, UTS and fatigue strength, with a joint efficiency of ~91% was achieved while the YS, UTS and fatigue strength of the DLWed joints were notably lower. The DSAWed joints and DLWed joints exhibited a higher strain hardening capacity in comparison with the FSWed joints and FLWed joints, respectively.