Uterine fibroids are common benign tumors of the reproductive organ and occur in approximately 50-80% of women of reproductive age. The pathogenesis of uterine fibroids is multifactorial and includes: sex hormones, genetic factors, cytokines, and oxidative stress. Objective: The aim of this study was to investigate the oxidative stress markers in tissue samples of women with uterine fibroids, with further analysis on size and menopausal status. Materials and Methods: Fifty-nine patients with the mean age 50.6 (35 premenopausal and 24 postmenopausal) who underwent standard gynecological procedures were recruited in the study. All women had histologically proven uterine leiomyoma. Samples were collected ex vivo immediately after resection. Glutathione peroxidase (GPX), catalase (CAT), and the ferric reducing ability of plasma (FRAP) were measured. Results: The activity of GPX was significantly higher in fibroid samples than in myometrium (0.070 +/- 0.042 vs. 0.057 +/- 0.027 U/mg of protein, p < 0.05), activity of CAT did not differ between samples (1.13 +/- 0.86 vs. 1.23 +/- 0.51 U/mg of protein, p > 0.05), and FRAP presented higher values in fibroid samples than in myometrium (4.58 +/- 6.29 vs. 3.04 +/- 3.81 mM Fe+2/mg of protein), but the difference was not statistically significant (p = 0.06). In the subgroups analyses, there were no statistically significant differences when comparing the activity of GPX, CAT, and FRAP in fibroid samples from pre- and postmenopausal women, as well as when comparing fibroid samples of small size (< 50 mm) and large size (≥ 50 mm) tumors. Conclusion: Oxidative stress markers are changed in fibroid tissue samples showing that oxidative stress may play an important role in this tumor formation, although without influencing menopausal status nor tumor size.