The strength and microstructure characteristics of the nugget in aluminum ally resistance spot welding were evaluated in this study with and without addition of rare earth elements Er, Ce. The strength was assessed using a small punch test mode and the microstructure was studied using an optical microscope, scanning electron microscope, and energy-dispersive spectroscope. Results indicated that the hardness and strength were 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 rare elements and its compounds were dispersed. This showed that parts of rare earth elements existed as solid solution in Al Matrix, part as the rare earth compounds. This improved that the elements not only can promote nucleation and refinement, but also can inhibit plastic deformation by hindering the dislocation movement. Thus they could play a strengthened role. The strengthening mechanism of the rare earth elements Er, Ce in the alloy nugget is mainly the second phase strengthening and fine grain strengthening.