The principal health problem in small ruminants is helminthiasis and the rapid development of nematode resistance to anthelminthics has limited the success of control in several countries, stimulating the search for alternatives. In this study, extracts of immature fruits of the mango Mangifera indica L. var Ubá were evaluated for inhibition of larval development and fecal egg count reduction in sheep naturally infected with gastrointestinal nematodes. In the phytochemical analyses, tannins and flavonoids were the metabolites identified. Aqueous extracts of immature fruits at 100 mg ml(-1) showed 100 % inhibition of larval development. The LC(90) of the extract was 35.9 mg ml(-1) and the in vivo anthelminthic efficacy at 0.740 g kg(-1) (BW, orally) was 53 %. The identification of larvae showed that 99.8 % were Haemonchus spp. In vitro and in vivo results indicate that this fruit could assist ovine nematode control.