Abstract: The strength and microstructure characteristics of the nugget in aluminum alloy resistance spot welding were evaluated in this study with and without addition of rare earth elements Er,Ce.The strength was assessed by a small punch test mode and the microstructure was studied with an optical microscope and energy-dispersive spectroscope.Results indicated that the hardness and strength increased about 10% after adding rare earth elements Er,Ce in the nugget.The grain of nugget zone was refined significantly.In the boundary and interior of the grain,a number of intermetallics were dispersed.The intermetallics can not only promote mucleation and refinement,but also hinder the dislocation movement.It was proved that rare earth elements could improve the properties of nugget significantly.