This study aimed to examine the possible association between the oxidative stress parameters and clomiphene citrate resistance in polycystic ovary syndrome. The demographic data, hormone profiles and oxidant and antioxidant values of 50 clomiphene citrate-resistant polycystic ovary syndrome patients (Group 1), 32 clomiphene citrate-sensitive polycystic ovary syndrome patients (Group 2) and 87 non-polycystic ovary syndrome patients (Group 3) were compared. The average age, follicle-stimulating hormone, oestradiol, thyroid-stimulating hormone and prolactin values of the three groups were found to be homogeneous. Ferroxidase, catalase and myeloperoxidase levels were determined to be lower in the clomiphene citrate-resistant group compared to clomiphene citrate-sensitive and non-polycystic ovary syndrome groups (p < .001). As a result, Polycystic ovary syndrome patients with clomiphene resistance had lower antioxidant (catalase and ferroxidase) levels compared to those who were sensitive to clomiphene and who did not have polycystic ovary syndrome. The myeloperoxidase levels also demonstrated the same trend, which might be due to a compensation mechanism.Impact Statement What is already known on this subject? In the literature, there are many studies evaluating the association between PCOS and oxidative stress. No research related to antioxidants in clomiphene citrate-sensitive and clomiphene citrate-resistant PCOS patients was found in the relevant literature. What do the results of this study add? In this study, the antioxidants catalase and ferroxidase were found to be lower in PCOS women compared to non-PCOS; however, they were the lowest in clomiphene citrate-resistant PCOS women. Interestingly, myeloperoxidase, which is a part of oxidative stress, was also found to be higher in the non-PCOS group.