Stryphnodendron adstringens (Martius) Coville (Leguminosae), popularly known as “barbatimão”, is a medicinal plant that grows in the central Savannas of Brazil. Decoctions or infusions of the stem bark are traditionally used by the native population of Brazil in the treatment of leukorrhea, diarrhea and as an anti-inflammatory medicine. The aim of this study was to evaluate the antigenotoxicity effect of ethanolic extract of barbatimão (EEB) against induced damage by mitomycin C (MMC) by the bone marrow micronucleus test in mice. Doses of EEB (50 mg/kg, 100 mg/kg e 200 mg/kg) and MMC (4 mg/kg) were administered simultaneously by intraperitonial injection (i.p.) in groups of 5 (five) animals for treatment. The positive control received a MMC i.p. (4 mg/kg) and negative control, distilled and sterilized H2O. Cytological preparations were done according Heddle (1973). For all the doses, micronucleated polychromatic erythrocytes frequency (MNPCE) was evaluated at period of 24 h. The obtained results showed no significantly inhibition of MNPCE frequency (mean = 28.6; SD = 1.67) in the dose of 50 mg/kg of EEB compared to positive control (mean = 30.6; SD = 2.70) (p > 0.05). However, the EEB in doses of 100 mg/kg (mean = 19.8; SD = 2.28) and 200 mg/kg (mean = 16.8; SD = 2.58) suppressed significantly the frequency of MNPCE induced by MMC (p < 0.05). Thus, the results indicated that the EEB exhibited antigenotoxic activity in bone marrow of mice.