Plastic deformation and dynamic recrystallization (DRX) behaviors of magnesium alloy AZ31B during thermal compression and extrusion processes were studied. In addition, effects of deformation temperature and rates on the microstructure and mechanical properties were investigated. The results show that the DRX grains nucleate initially at the primary grain boundaries and the twin boundaries, and the twinning plays an important role in the grain refinement. The DRX grain size depends on the deformation temperature and strain rate The average grain size is only 1 μm when the strain rate is 5 s-1 and temperature is 250 ℃. It is also found that the DRX grain can grow up quickly at the elevated temperature. The microstructure of extruded rods was consisted of tiny equal-axis DRX grains and some elongated grains. The rods extruded slowly have tiny grains and exhibit good mechanical properties. Plastic deformation and dynamic recrystallization (DRX) behaviors of magnesium alloy AZ31B during thermal compression and extrusion processes were studied. In addition, effects of deformation temperature and rates on the microstructure and mechanical properties were investigated. The results show that the DRX grains nucleated initially at the primary grain boundaries and the twin boundaries, and the twinning plays an important role in the grain refinement. The DRX grain size depends on the deformation temperature and the strain rate The average grain size is only 1 μm when the strain rate is 5 s-1 The microstructure of extruded rods was consisted of tiny equal-axis DRX grains and some elongated grains. The is also found in the DRX grain can grow up quickly at the elevated temperature. exhibit good mechanical properties.