The static and fatigue strengths of mechanically clinched, self pierce riveted and resistance spot welded joints in aluminium alloy A5052-H34 sheets were investigated. In the static tension-shearing test, self pierce riveted, resistance spot welded and mechanical clinched joints were tested in order of the maximum load. The endurance ratio of the sheets joined by the mechanical clinching and self pierce riveting were larger than that of the sheets joined by resistance spot welding owing to the work-hardening and slip at the interface between the sheets, i.e. the fatigue characteristic of mechanical joining processes was better than that of the welding processes involving metallurgical bonding. To increase the maximum joint load for mechanical clinching, a step punch was proposed. In the mechanical clinching using the step punch, the wall thickness in the side wall of the punch was increased by the compression of the step. The maximum static load and endurance ratio for mechanical clinching using a step punch were increased by 21% and 45%, respectively.