SiC particles reinforced Mg base composites were extruded at different temperatures and extrusion ratios. The effects of particles on dynamic recrystallization (DRX) of Mg matrix during hot extrusion were investigated. The results reveal that particle deformation zone (PDZ) is formed near a particle during hot deformation, and the PDZ is a characteristic of fine DRX grains in the composites extruded at lower temperatures. Particles promote DRX nucleation of Mg matrix during hot extrusion which may be attributed to high density dislocations and large orientation gradients in PDZ. Particles promote the growth of fine DRX grains until PDZ is consumed by DRX grains. On the contrary, at the stage when DRX grain boundaries contact with particles, particles pin grain boundaries and then retard grain growth.