Al/Cu lap joint sheets were fabricated by magnetic pulse welding (MPW). A strong lap joint was achieved at a discharge energy more than 0.9 kJ. When the welding at an adequate amount of discharge energy, weld interface showed wavy morphology. Weld width of the lap joint sheets tend to increase with increasing of discharge energy for welding. SEM and EDS results indicated that intermediate phase was discontinuously observed at the weld interface due to localized melting, but no significant contrast of oxides was exhibited. A metal jet was observed around weld areas on Al and Cu sheets. TEM observation indicated that the intermediate phase consisted of CuAl2 with fine grain size less than 10 nm. Work hardening at the welding interface and grain refinement of Cu at wave front were recognized. These results indicated that weld interface was strengthened by work hardening and grain refinement. It was considered that strong lap joint of Al and Cu sheets by MPW resulted from an increasing of weld width, the anchor effect, and strengthening of weld interface due to work hardening and grain refinement.