Abstract: Research on pollen abortion of alfalfa (Medicago) and cytological observation of factors affecting it was carried out for two years in four different ecological regions of alfalfa including eight observation points in Xinjiang. 1) The pollen abortion percentages differed significantly between the different ecological regions and between different alfalfa plots in the same region. In 2008, the pollen abortion percentage of different alfalfa plots were: Tacheng (20.05±5.33)%,(23.41±3.76)%, (29.80±5.45)%, (P<0.05); Yili(28.34±3.19)%; Hutubi(15.57±2.18)%, (31.47±4.59)%, (P<0.05);Hetian(20.79±2.89)%, (26.51±4.74)%, (P<0.05). 2) The alfalfa pollen abortion percentages were significantly different between different years at the same observation point. In 2007, the alfalfa pollen abortion percentage of M. varia cv. Xinmu No.1 and M. sativa cv. Xinjiang Daye were (37.96±2.10)% and (38.70±2.40)% respectively in the Hutubi alfalfa seed base, and in 2008 the alfalfa pollen abortion percentages were (15.57±2.18)% and (31.47±4.59)%, (P<0.01). 3) At the group level, pollen abortion percentages did not show significant differences at different stages of anthesis, but did have a significant differences between single flowers distributed on the same alfalfa plant, but with no obvious location or time effect. 4) From the cytological characteristics of pollen development, there was no significant limiting factor affecting pollen abortion during pollen development. The fluctuatation of the tapetum degradation period was influenced by environmental factors leading to differences of pollen abortion of the same alfalfa variety between different ecologic region and years.