OBJECTIVE To evaluate the hydroethanolic extract toxicity, obtained from Tropaeolum majus L. (TM) on mouse testicular tissue. METHODS In this experimental study, we used 32 male NMRI mice. The experimental groups received 75, 375 and 750 mg/kg of TM extract, respectively. Twenty-four hours after the last experimental day, serum samples were collected for hormonal measurement. Then, the cauda of epididymis and testis were removed for sperm count and histopathological assessments. RESULTS Testosterone serum and testicular levels decreased in 750 mg/kg in the treated group when compared to the control animals (1.65±0.25; p=0.041 and 98.83±8.67; p=0.034 respectively). Histopathological criteria such as epithelial vacuolization (9.3±1.1; p=0.034), sloughing (4.3±0.4; p=0.027) and detachment (12.2±0.9; p=0.031) of germ cells were significantly increased in 750 mg/kg in the treated mice. In addition, there were no significant changes in histopathological criteria; sperm head numbers, Johnsen's scoring, and morphometry assessments were carried out in the 75 and 375 mg/kg treated mice. At the dose of 750 mg/kg, the seminiferous tubule diameter (193.2±4.6; p=0.019), seminiferous epithelium height (139.2±5.1; p=0.023), and maturation arrest were significantly decreased in this group. CONCLUSIONS In conclusion, TM extract has toxic effects on the mouse testicular tissue in high doses. Hence, we recommend caution concerning its consumption by patients with reproductive problems.