Abstract: Pulsed laser welding of in situ TiB2 particulate reinforced ZL101 aluminum matrix composites was carried out. The effects of pulse frequency on the formation of bead and microstructure were studied. The results show that the formation of bead is good, and the porosity is decreased due to the effect of stirring of pulsed laser on the molten pool. The clusters of TiB2 get finer and distribute more homogeneously in the bead than that in the base metal. The stirring effect decreases when the pulse frequency is up to 200 Hz so that much porosity occurs and the clusters get larger. Moreover, the penetration depth is decreased with the pulse frequency increasing. The grain is very fine in the bead and TiB2 particles are located at the grain boundary. The values of hardness are uniform in the bead, higher than that in the base metal. There is no interface reaction to produce brittle products between the TiB2 and Al matrix so that it keeps the strengthening effects of reinforcement.