Introduction: Cancer and testis antigens (CTA) represent a group of aberrant proteins that are expressed in different types of cancer. They are of interest as markers of malignant tumors and targets for the development of immunotherapy. Until now, the association of CTA expression with the response to first-line platinum-based chemotherapy and the duration of the response has not been analyzed in patients with high-grade serous ovarian cancer (HGSOC). The aim of the research was to analyze the expression of different CTAs (MAGE-A1, MAGE-A10, multi- MAGE and NY-ESO-1) in HGSOC samples using the immunohistochemical method and to examine the association of this expression with response and durtion of response to first-line chemotherapy based on platinum. The association of CTA expression with the length of survival to disease progression (PFS) and the length of overall survival (OS) was analyzed. Materials and methods. The study included 93 patients with histologically confirmed HGSOC FIGO stage III and IV, treated at University Hospital Split and general Hospital Zadar from January 1, 1996 to December 31, 2013. All patients underwent surgery and were then treated with first-line platinum-based chemotherapy. The variables were age, FIGO stage of the disease, size of the remaining tumor after primary surgery, number of chemotherapy cycles, PES and OS. Immunohistochemical staining with monoclonal antibodies to MAGE-A1, MAGE-A10, multi-MAGE and NY-ESO-1 was performed mechanically on the automated Ventana BenchMark Ultra autostainer. Brown cytoplasmic and/or nuclear staining, regardless of staining intensity, with a threshold value of ≥10% tumor cells was considered positive. The Statistical Package for the Social Sciences (SPSS) software version 20 for Windows was used for statistical data processing. Results. MAGE-A10 expression statistically significantly predicts resistance to first-line platinum-based chemotherapy (p<0.001) and poor response to platinum treatment (p=0.005). MAGE-A10 expression in tumor cells is associated with significantly worse PFS (p <0.001) and OS (p <0.001). No correlation was found between the other examined CTAs with response to first-line platinum-based chemotherapy, platinum sensitivity, PFS and OS. Conclusion. This is the first study to establish an association between MAGE-A10 expression and chemosensitivity in subjects with HGSOC receiving platinum-based chemotherapy. MAGE-A10 could become a marker of a more aggressive phenotype of high-grade serous ovarian cancer and a potential target for targeted immunotherapy when there is no response to platinum-based chemotherapy.