Objective: To investigate the therapeutic effect and the related mechanism of oridonin on mice with prostate cancer. Methods: Sixty BALB/C male nude mice were selected. A model of RM-1 cell transplantation tumor of prostate cancer was built by the subcutaneous inoculation of RM-1 cells. After that, those 60 experimental mice were randomly divided into groups A, B and C. Each group had 20 mice. Mice in group A were treated with 0.2 m L of normal saline(0.9%) by intraperitoneal injection once a day; mice in group B received intraperitoneal injection of 1.875 mg/m L of oridonin once a day; and mice in group C received intraperitoneal injection of 7.5 mg/m L of oridonin once a day. Mice in the three groups were treated uninterruptedly for 5 weeks and were all killed. Then, tumors were excised and weighed to calculate their growth inhibitory rate, volume increment and anti-tumor rate. Thymus and spleen of mice in the three groups were collected to calculate the thymus and spleen index. Immunohistochemical staining was applied to observe the expression of caspase-3 in prostate cancer tissue of mice of the three groups. Results: The qualities and volume increment of tumors in groups B and C were significantly lower than those of group A(P < 0.05); the qualities and volume increment of tumors in groups C were evidently lower than those of group B(P < 0.05); the tumor volume increment and anti-tumor rate in group C were obviously higher than those of group B(P < 0.05); the thymus and spleen indexes of groups B and C were distinctly higher than those of group A(P < 0.05); comparison of the thymus and spleen indexes between group B and group C showed no statistical differences(P > 0.05). Immumohistochemical staining revealed that the caspase-3 protein in prostate cancer tissue of mice of group A expressed negatively with colourless or light-colored karyon; while the caspase-3 protein in prostate cancer tissue of mice of group B expressed positively with dark-colored karyon, centralized distribution and granular sensation; and the caspase-3 in prostate cancer tissue of mice of group C showed strong positive expression with big and darker colored karyon and dense distribution. Conclusions: Oridonin can inhibit the growth of RM-1 prostate cancer cells effectively and have great therapeutic effects on RM-1 cell transplantation tumor of prostate cancer. Objective: To investigate the therapeutic effect and the related mechanism of oridonin on mice with prostate cancer. Methods: Sixty BALB / C male nude mice were selected. A model of RM-1 cell transplantation tumor of prostate cancer was built by the subcutaneous inoculation of RM-1 cells. After that, those 60 experimental mice were randomly divided into groups A, B and C. Each group had 20 mice. Mice in group A were treated with 0.2 m L of normal saline (0.9%) by intraperitoneal injection once Mice in the group B received intraperitoneal injection of 1.875 mg / m L of oridonin once a day; and mice in group C received intraperitoneal injection of 7.5 mg / m L of oridonin once a day. Mice in the three groups were treated uninterruptedly for 5 weeks and were all killed. Then, tumors were excised and weighed to calculate their growth inhibitory rate, volume increment and anti-tumor rate. Thymus and spleen of mice in the three groups were collected to calculate the thymus and spleen index. Immu nohistochemical staining was applied to observe the expression of caspase-3 in prostate cancer tissue of mice of the three groups. Results: The qualities and volume increment of tumors in groups B and C were significantly lower than those of group A (P <0.05) ; the qualities and volume increment of tumors in groups C were evidently lower than those of group B (P <0.05); the tumor volume increment and anti-tumor rate in group C were obviously higher than those of group B (P <0.05) ; the thymus and spleen indexes of groups B and C were distinctly higher than those of group A (P <0.05); comparison of the thymus and spleen indexes between group B and group C showed no statistical differences (P> 0.05). Immumohistochemical staining revealed that the caspase-3 protein in prostate cancer tissue of mice of group A expressed negatively with colored or light-colored karyon; while the caspase-3 protein in prostate cancer tissue of mice of group B expressed positively with dark-colored karyon, ceCentralized distribution and granular sensation; and the caspase-3 in prostate cancer tissue of mice of group C showed strong positive expression with big and darker colored karyon and dense distribution. Conclusions: Oridonin can inhibit the growth of RM-1 prostate cancer cells effectively and have great therapeutic effects on RM-1 cell transplantation tumor of prostate cancer.