Abstract: Objective To investigate the relationship between the change of circulating tumor cells （CTC） in peripheral blood and the chemotherapy effect of ovarian cancer. Methods A total of 28 ovarian cancer patients treated with chemotherapy in our department from February 2013 to April 2015 were enrolled in this study. Venous blood samples of 4 ml were collected from them before and after chemotherapy. The CTC in peripheral blood were purified by negative selection using immunomagnetic， and detected by immune fluorescence in situ hybridization （imFISH）. The CTC number over 2 in 3.2 ml was defiend as positive. The RECIST 1.0 criteria was used to assess the efficiency of chemotherapy， the relationship between the change of CTC before and after chemotherapy to the therapeutic effect of chemotherapy was studied. Results The positive rate of CTC before chemotherapy was 60.71%（17/28）， which was related with tumor stage （P=0.017） and CA125 levels （P=0.049）， while it of CTC detected after chemotherapy was 25％（7／28）. According to the status of CTC before and after chemotherapy，the patients were divided into 4 groups，that is，positive to positive，positive to negative， negative to positive and negative to negative groups.Their efficiencies was 80％（4／5），83.33％（10／12），0（0／2）and 88.89％（8／9） respectively, with significant difference（P=0.045）. Conclusion The changes of CTC before and after chemotherapy has a certain relationship with the efficiency to chemotherapy. CTC can be regarded as a predictor for evaluating chemotherapy.