In　present　study,　50　μm　thick　Ti/Cu　pure　metal　ultra-thin　foils　are　successfully　lap-welded　by　a　nanosecond　fiber　laser.　The　joints　with　adjustable　depths　are　obtained　by　controlling　the　laser　energy　input　precisely.　The　microstructure　and　mechanical　properties　of　Ti/Cu　joints　with　different　depths　are　well　analyzed,　respectively.　In　the　joint　with　smaller　penetration　depth　of　10　μm,　thin　band-like　Ti/Cu　intermetallic　compounds　(IMCs)　are　formed,　while　in　the　joint　with　a　larger　penetration　depth　of　40　μm,　thicker　band-like　Ti/Cu　IMCs　and　sizable　bright　dendritic　Ti2Cu　phases　are　formed,　since　more　Cu　element　are　involved　in　the　chemical　reaction　in　the　joint　with　penetration　depth　increasing.　The　tensile　test　results　show　that　the　weld　with　10　μm　penetration　depth　has　the　best　tensile　strength　up　to　240　MPa,　which　is　mainly　due　to　less　IMCs　and　low　heat　input　in　the　weld.　In　addition,　the　fracture　mode　of　the　joint　is　classified　into　two　models,　including　brittle　quasi-cleavage　fracture　on　the　Ti　side　fusion　zone　(FZ)　and　ductile　fracture　on　the　Cu　heat　affected　zone　(HAZ),　respectively,　depending　on　the　penetration　depth　above　or　below　30　μm.　©　2023　The　Society　of　Manufacturing　Engineers