This paper describes a novel in vivo study of Cymbopogon citratus (lemon grass) to assess its anthelmintic activity. To this end, C57BL/6 mice were separated into three groups: G1: uninfected; G2: negative control infected with Heligmosomoides polygyrus bakeri and administered with 3% dimethyl sulfoxide (DMSO); and G3: infected with H. polygyrus bakeri and treated with C. citratus aqueous extract (50mg/kg). The extract and H. polygyrus bakeri were administered via gavage and the anatomo-histopathological evaluation of the animals took place after necropsy and organ removal. In addition, the number of eggs per gram of feces (epg) and of adult parasites in the small intestine of each animal, as well as blood cell counts, were assessed. The in vivo assay revealed a reduction in the epg (54%), number of adult nematodes (89%), number of eosinophils, and intestinal lesions in mice treated with C. citratus. These results suggest that the crude aqueous extract of C. citratus at the dose evaluated here has anthelmintic and possibly anti-inflammatory properties, given its effectiveness against gastrointestinal H. polygyrus bakeri nematodes and the recovery of damaged tissues. Therefore, this plant shows potential to control gastrointestinal nematodes.