Abstract: Objective To study the function of the rennin-angiotensin-aldosterone system (RAAS) under high altitude hypoxia and to investigate effects of high altitude hypoxia on the angiotensin conversion enzyme 2 (ACE2) mRNA and protein expressions in right ventricle in SD rats.Methods Forty male adult Sprague-Dawley (SD) rats were divided randomly into 4 groups: group A with one day hypoxia (moved from 5 to 2 700 m above sea level in one day), group B with three days hypoxia(moved from 5 m to 4 500 m above sea level in three days), grou C with 30 day's hypoxia(raised at 4 500 m above sea level for 30 days), and group D-the control(raised at the palce of 5 m above sea level).The plasma rennin activity(PRA), serum angiotensin(AT), and serum aldoxterone(ALD) of the rats were detected with radio immunoa ssay.ACE 2 mRNA and protein in the tissue of right ventricle were measured by reverse transcriptase (RT) PCR and western blot.Results The contents of PRA, AT, and ALD were 5.15±0.86 ng/mL·h, 92.10±10.25 pg/mL, and 85.60±29.40 pg/mL for group A, 7.12±0.31 ng/mL·h, 160.53±10.84 pg/mL, and 56.30±25.23 pg/mL for group B, and 5.37±0/28 ng/mL·h, 127.45±30.6 pg/mL, and 82.54±26.78 gp/Ml for group C, respectively.The hypertrophy of right ventricle was observed and ACE 2 mRNA and prote in synthesis were inc reased in group C compared with those of the control group(P<0.01).Conclusion RAAS is correlated with the acclmiatization of high a ltitude hypoxia environment and has important effect.ACE2 mRNA and prote in synthesis are increased under high altitude hypoxia environment, suggesting that ACE2 may play a role in high altitude hypoxic adaptation of the heart.