Abstract: A large group of commercial broilers that were raised according to AA feeding condition were divided into hypertension and ascites group(group S), hypertension group(group M) and control group(group C). The activities of iNOS and cNOS in lung and serum of boilers in group S, M and C were measured at the age of 21,28,35 and 42 days. AHI, WH/BW, mPAP and nitric oxide (NO) in serum were measured as well. Results were as follows: (1) From the age of 28 days, the WH/BW of group S and group M and the NO level in serum of group S were higher or significantly higher than that of group C（P＜0.01 or P＜0.05）; (2) The cNOS activity in lung of group S was lower or significantly lower than that of group C（P＜0.01 or P＜0.05）; (3) At 21,35 and 42 days old, the iNOS activity in lung of group S was higher or significantly higher than that of group C（P＜0.01 or P＜0.05）; (4) From the age of 28 days, the cNOS and iNOS activities in serum differed significantly or very significantly between group S and group C（P＜0.01 or P＜0.05）; (5) The iNOS activity was lower or significantly lower than cNOS activity in serum of group C at the age of 21,35 and 42 days（P＜0.01 or P＜0.05）. It was suggested that the changes of cNOS and iNOS activities play a role in the development of PHS.