Abstract: To probe the activity of inducible nitric oxide synthase (iNOS) in liver , the concentration of nitric oxide (NO) in serum and its inhibition or killness on coccidia in Eimeria stiedai infected rabbits, the infected rabbits were injected with the substrate of nitric oxide synthase L-arginine (L-Arg) and the inhibitor of inducible nitric oxide synthase L-aminoguanidine (L-AG) through the abdominal cavity. Then the activity of iNOS in liver , the concentration of NO in serum，the coccidian oosysts per gram feces (OPG), the anatomic structures and microscopic pathological changes of rabbits’ livers and their scores were studied. The results showed that : ① The activity of iNOS of the uniform slurry of the liver and the concentration of NO in serum increased gradually after infection, and that in control group, L-arginine group, and L-AG group reached the top at 12 days after infection, then decreased gradually and reached the level before infection at ~23 days; ② L-Arg can enhance the activity of iNOS and the release of large amount of nitric oxide, consequently it inhibit or kill Eimeria stiedai and ease the pathological changes caused by Eimeria stiedai; while L-AG decreased the activity of iNOS and reduce NO production in vivo, so that it aggravates the pathological changes caused by Eimeria stiedai. The results showed that NO and iNOS participate in the infection process of Eimeria stiedai in rabbit and NO plays an role of inhibition or killness on coccidia of E.stiedai.