Abstract: Regulated Deficit Irrigation (RDI) is known to have higher water use efficiency, and higher fruit yield with better quality. Field experiments were conducted during 2009 and 2010 in Korla city, Xinjiang autonomous region, to investigate the effects of RDI applied in different growth stages and with different levels of water deficit on vegetative, fruit growth and yield of mature fragrant pear trees of 24 years old. The experimental treatments involved moderate and severe water deficit, in either the cell division period or in the slow fruit growth period or in both periods. Trickle irrigation, with 2 driplines, one on each side of the trees was adopted. The moderate RDI used 60% and the severe used 40% replacement of US Class A pan evaporation, respectively. Irrigation amount during non-deficit stages was the same as in the control treatment. The control treatment was irrigated at 80% of pan evaporation during the whole growth season and all treatments were irrigated weekly. The results showed that the water deficit applied during both cell division and/or slow fruit enlargement stage inhibited the vegetative growth. Compared with the control, the summer pruning of the RDI treatments was reduced by 8.4%-43.2%. In both years, as compared with the control, the severe water deficit irrigation during cell division stage significantly increased yield by 15.5%-19.2%, and reduced the irrigation water by 9.7%-8.1%. The yield of moderated water deficit irrigation in slow fruit enlargement stage was increased by 14.0%-18.0%, and the irrigation water was reduced by 13.2%-11.3%. The yield of severe water deficit irrigation during both cell division and slow fruit enlargement stages was decreased by 15.4%-13.2%, and the irrigation water reduced by 34.7%-28.4%. Fruit quality had no significant differences among the treatments. The results are meaningful to guide the irrigation management of mature Korla fragrant pear trees.