Objective To identify an effective auxiliary therapy for epithelial ovarian cancer. Methods Progesterone acetate given at 250 mg intramuscularly twice a week for 1 month followed by increased administration to 500 mg intramuscularly every two weeks for 3 years was used in combination with platinum based chemotherapy to treat patients with epithelial ovarian cancer as a first-line therapy. Prognoses of the patients receiving progesterone combined with chemotherapy (progesterone group) and those receiving chemotherapy only (control group) were compared. Results Three-year recurrence and survival conditions of the progesterone and control groups were as follows. Stage Ⅰa: no patient relapsed or died in either group. Stage Ⅰb-Ⅰc: three-year recurrence rates were 14.2% and 37.5%, respectively ( P =0.2845); three-year survival rates were 92.3% and 87.5% ( P =0.7221). Stage Ⅱ: 1 patient relapsed and died among the 3 patients in the progesterone group; among the 4 patients in the control group, 1 patient relapsed, none died. Stage Ⅲ: three-year recurrence rates were 30.8% and 64.3%, respectively ( P =0.1170); three-year survival rates were 85.7% and 42.9%, respectively ( P =0.005). Stage Ⅳ: 4 patients relapsed and 1 patient died among the 7 patients in the progesterone group; both the patients in the control group relapsed and died. Conclusions The results indicated that progesterone combined with platinum based chemotherapy as a first-line therapy may improve the prognosis of advanced epithelial ovarian cancer, but would not change the prognosis of early stage epithelial ovarian cancer.