The　dissimilar　AZ31B/AZ61　Mg　alloy　joints　were　fabricated　by　pulse　current-assisted　friction　stir　welding　(PCaFSW).　The　maximum　tensile　strength　and　elongation　were　314.28　MPa　and　13.66%,　respectively.　A　micro　interlocking　structure　was　formed　and　the　grain　refinement　effect　was　enhanced　by　the　PCaFSW　process,　which　was　improved　relative　to　that　in　the　conventional　FSW.　The　enhanced　strength　and　plasticity　with　increasing　pulse　current　were　attributable　to　the　grain　refinement,　weakening　of　texture　strength,　formation　of　nano-scale　precipitates　and　increase　of　short　dislocation　lines.　The　fracture　mode　was　transformed　from　a　brittle　fracture　mode　to　a　combined　fracture　mode　of　brittle　and　ductile　fractures.