The　demand　for　high-quality　nickel-titanium　(NiTi)　shape　memory　alloy　(SMA)　and　stainless　steel　(SS)　welded　structures　has　led　to　significant　challenges　in　fusion　welding　technology,　which　is　largely　influenced　by　filler　materials.　This　study　explores　the　application　of　CoCrNi　medium　entropy　alloy　and　CoCrNiFe　high　entropy　alloy　as　filler　materials　for　laser　lap　welding　of　NiTi　SMA　and　304　SS.　A　self-fusing　joint　was　produced　for　comparison.　The　results　demonstrate　that　the　interface　zone　on　the　NiTi　side　was　the　weakest　area　regarding　cracking　defects　in　NiTi/304　SS　lap　joints.　However,　using　CoCrNi　and　CoCrNiFe　fillers　effectively　eliminated　cracking　defects　by　considerably　suppressing　the　formation　of　brittle　FeTi　and　Fe2Ti　intermetallic　compounds　(IMCs).　The　average　microhardness　value　of　the　weld　zone　without　filler　was　higher　than　with　CoCrNi　and　CoCrNiFe.　Furthermore,　the　addition　of　CoCrNi　and　CoCrNiFe　fillers　to　NiTi/304　SS　lap　joints　resulted　in　a　substantial　increase　in　tensile　properties,　with　tensile　strength　reaching　196　±　39　MPa　without　filler,　319　±　25　MPa　with　CoCrNi,　and　377　±　33　MPa　with　CoCrNiFe,　respectively.　©　2024,　International　Institute　of　Welding.