Si–Al–Y co-deposition coatings were prepared on a Ti–Al alloy by pack cementation process at 1050 for 4 h. The effects of pack Y2O3 content(from 0 to 5 wt%) on the microstructure and constituent phases ofthe co-deposition coatings were studied, the wear resistance of the substrate and the coated specimens were also compared at 600 ?C in air. The results showed that the pack Y2O3 content imposed strong influences on both coating structures and phase constituents. The coatings prepared with the pack mixtures containing 1 and 2 wt% Y2O3 were composed of an TiSi2 out layer, an (Ti, X)5Si4 and (Ti, X)5Si3(X represents Nb and Cr)middle layer, an TiAl2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi2,(Ti, X)5Si4 and (Ti, X)5Si3 in the out layer of the coating prepared with the pack mixture containing 3 wt% Y2O3. Moreover, (Ti, X)5Si4 and (Ti, X)5Si3 phases were observed in the outer layers of the coatings prepared with the pack mixtures containing 0 and 5 wt% Y2O3. The coating growth could be catalyzed obviously when the content of Y2O3 in the pack mixtures increased from 1 to 2 wt%, but this phenomenon was not observed when further increased the pack Y2O3 content to 3 or 5 wt%. Si–Al–Y co-deposition treatment improved the surface hardness and wears resistance of the Ti–Al alloy significantly. The wear resistance of the tested samples could be sorted in the following sequence: 1% Y2O3-coating > no RE-coating > bare Ti–Al alloy