Abstract: The resistance spot welding of the Al₂O₃ fiber reinforced Al-matrix composites (MMCs) was conducted using a micro-type capacitor discharge welding machine and the microstructural morphology of the joint was investigated. The results showed that a regular, flat nugget was formed in the joint and the microstructural transition from nugget to matrix was rather well. Due to the very short welding time and high cooling rate, the eutectic Si was refined remarkably. The tiny eutectic Si particles distributed uniformly in the Al-matrix, resulting in microstructure different from the MMCs. Small quantity of Al₂O₃ fibers were broken down to some extent, while most of them remained their original morphology, distributing in the nugget matrix randomly. It was considered an effective way to eliminate the porosity and improve the joint quality, i.e. increasing electrode pressure properly, removing hydrogen from MMCs and holding the MMCs dry.