Abstract: [Objective] To observe changes of plasma arginine vasopressin（AVP） levels and its relationship with altitude hypoxic acclimatization in rats under high altitude hypoxia.[Method] Fifty male SD rats were randomly divided into five groups（A,B,C,D and E）,and control group（Xi＇an region,altitude of 5 m） was also set up.The experimental groups were transported to test area by car.The rats in the group A were taken to Golmud region of Qinghai Province（altitude of 2 700 m） within 24 h.The rats in the group B were taken to Tanggula region of Tibetan area（altitude of 5 000 m） within 48 h.The rats in groups C,D and E were taken to Naqu region of Tibetan area（altitude of 4 500 m） within 72 h,1 week and 1 month,respectively.All the rats were sacrificed at different time points,and plasma AVP levels were determined by radioimmunoassay.The results were compared with those of the control group.[Result] The plasma AVP level increased after they entered the plateau.It then decreased and reached a valley after 48 h.Subsequently,it gradually picked up after 1 week and reached a peak after 1 month.[Conclusion] Under high altitude hypoxia,plasma AVP level changes with prolongation of hypoxia,maybe due to degree of hypoxia and altitude hypoxic acclimatization.