Introduction: The effect of intrauterine administration of Momordica charantia L. (MC) extract on oxidative changes and pregnancy rate in infertile cows was investigated. Material and Methods: Endometrial smear specimens were taken from 40 cows with fertility problems for cytological examination, and the cows were randomly divided into two groups: group I (n = 20) was subjected to intrauterine administration of 40 mL (0.25 g/mL) of MC extract, group II (n = 20) was subjected to intrauterine administration of 40 mL of pure olive oil. Blood samples were taken starting from the day of administration of MC extract or olive oil (day 0) and then for three weeks at weekly intervals (days 7, 14, 21). Blood serum samples were evaluated for total antioxidant capacity (TAS), total oxidant level (TOS), oxidative stress index (OSI), lipid hydroperoxide (LOOH), and nitric oxide (NO) levels. In addition, on the 14th day following treatment, two doses of PGF2 alpha were administrated to all cows at 14-day intervals. Following the second PGF2 alpha administration, insemination and GnRH administration was performed at the 60th h after PGF2 alpha treatment. Smear samples were stained with Giemsa and immunohistochemically to determine cytological changes and inflammatory status. Results: According to cytological findings, subclinical endometritis was a prevalent disorder in cows with infertility problem (82.5%; 33/40). Additionally, 60.6% (20/33) of the cows with subclinical endometritis had acute inflammation, whereas remaining 13 cows had chronic endometritis. Of the cows with subclinical endometritis, 50% (8/16) and 35% (6/17) became pregnant in group I and II, respectively (P > 0.05). Although the oxidative stress parameters showed similarities between both groups (P > 0.05), there was a significant difference (P < 0.001) between the groups in terms of mean NO and LOOH levels (NO - 31.20 +/- 11.38 vs 44.53 +/- 11.50 mu mol/L and LOOH - 1.22 +/- 0.37 vs 1.89 +/- 0.36 mu mol/L). Conclusion: The obtained results indicated that MC administration, especially in the presence of active inflammation, may improve the pregnancy rate by positive reduction of oxidative changes.