Abstract: Objective:To investigate the effects of L-arginine on nitric oxide（NO） and the expression of iNOS in the airway inflammation of asthma.Methods:the rat models of asthmatic inflammation were established by sensitizing and then challenging the animals with ovalbumin.The 32 animals were randomly divided into control group,sensitized group,L-Arginine control group as well as sensitized and L-Arg-treated group equally.iNOS impression was observed by using immunohistochemistry method,and The nitric oxide concentration was detected by the activated cadmium reduction method.Results:iNOS expression in athmatic rats was positively increased compared with that of the control group,nitric oxide concentration was obviously increased correlated with the blood gas getting worse.In sensitized and L-Arg-treated group,nitric oxde concentration was also increased while There was no statistically difference in the impression of iNOS and blood gas.Conclusions: It was indicated that a suitable levels of L-arginine can influence the production of nitric oxide while not change the expression of iNOS,L-arginine may inhibit the attack of asthma by promoting intrinsic NO induced by cNOS not iNOS.