Abstract: The inhibitory effect of Zhu-ling（Polyporus umbellatus）on urinary bladder carcinogenesis in rats treated with N-butyl-（4-hydroxybutyl）nitrosamine（BBN）was evaluated.Female Wistar rats were given at total dose of 2160mg BBN by means of gastric intubation（90mg,twice a week over a period of 12 week）.Animals were fed either placebo diet or a diet supplemented with Zhuling from the beginning of gastric intubation to the end of the experimental.Animals were killed at the 30th week after the initial gastric intubation.In comparison with the rats fed placebo diet, Zhu-ling significantly reduced the incidence,number and severity of the urinary bladder tumors （P＜0.01）without any toxicity.