Aim:To study the inhibition effects of 5 Fu on S 180 tumor bearing Yuyi hairless mice.Methods: Twenty five Yuyi hairless mice and 25 Kunming mice were randomly allocated into 4 groups after being loaded with S 180 cells, 2 were control groups, and the other 2 were experiment groups.Experiment groups were injected 5 Fu.The tumor weight were measured after 9 days. Results: The tumor weight of Yuyi hairless mice and Kunming mice in experiment groups were ( 0.93± 0.38) g and (0.23±0.08) g,respectively, and the corresponding control groups were (2.89±1.15) g and ( 2.56 ±0.78) g,respectively.The inhibition rates for hairless mice and Kunming mice were 67.7% and 91.0%,respectively.There were significant difference between 2 control groups and 2 experiment groups ( P 0.01 or P 0.05).Conclusion: 5 Fu has satisfactory antitumor effects with Yuyi hairless mice.