The influence of subrapid solidified processing parameters on the microstructure characteristic and grain refining efficiency of Al-5Ti-1B master alloy has been studied. The results show that the mean size of Al 3 Ti particles in Al-5Ti-1B master alloy decreases significantly after copper mould die casting. The morphology of Al 3 Ti particles changed from plate-like to blocky and petaloid. Compared with conventional Al-5Ti-1B master alloy, the phase constitution of subrapidly solidified Al-5Ti-1B master alloy does not change, and the improved master alloy shows a better grain refining efficiency. The microhardness of the pure aluminium refined by conventional and improved Al-5Tu-1B obeys the Hall-Petch relation, and the material constant k H is in the range of 84?02-91?80 MPa mm 1/2 . The mechanisms of grain refinement of aluminium by inoculation with improved Al-5Ti-1B master alloy are discussed based on the duplex nucleation theory and growth restriction effects in aluminium alloys.