Inhibition effects, control probabilities and pathology tissue changes of mouse transplanted tumors S₁₈₀ after irradiation with 50 MeV/u ¹²C⁶⁺ ions are reported. Doses of single irradiation were 0.5, 1, 2, 5, 10, 20, 40 Gy, respectively, at a dose rate of 3 Gy/min. Observing time was 24 days. The results show that each group had significant inhibition action on S₁₈₀ tumors and all inhibitory probabilities were more than 90%; the initial time of inducing tumor inhibition effects were within one week in high dose groups (20, 40Gy), and after two weeks in medium dose groups (5. 10 Gy) and low dose groups (0.5, 1, 2Gy); also, inhibitory effects in high dose groups were obviously greater than other groups (p <0.05); tumor control probabilities were different in each group, those in high dose groups (20, 40 Gy) were higher and TCD₅₀ (50% tumor control dose) was 20 Gy; the results for curing tumors are different in different doses; pathology inspection presented here were tumor tissue necrosis and degeneration in each dose group and they depended on doses.