Abstract: In this study, the rule of phenotypic change of smooth muscle cell (SMC) in the media of pulmonary arterioles was investigated during the development of ascites syndrome (AS) induced by excess salt in broiler chickens. One hundred male Arbor Acres broilers at day 8 were randomly divided into control group(C) and treated group (T). Chickens in the treated group were supplied with drinking water added 0.30% NaCl, and other factors were the same as that in control group. Lung samples of 5 randomly selected birds per group were collected to make routine paraffin section at 15，22，29，36，43 and 50 days respectively. Expression of α-SM-actin (phenotype marker protein of SMC) was determined by immunohistochemistry staining and image analysis program. The results suggested that there was dynamic phenotypic change of SMC in the media of pulmonary arterioles of broiler chickens in the control group. At day 22 SMC changed from contractile phenotype to proliferative phenotype, and did again from proliferative phenotype to contractile phenotype with in different outer diameter pulmonary arterioles at different time. Excess salt accelerated change of SMC from contractile phenotype to proliferative phenotype, and phenotypic change of SMC in pulmonary arterioles with 20-50 μm diameter was affected mostly and may play an important role in the development of AS.