Antitrypanosomal activity of crude 50% ethanolic extract of Xanthium strumarium leaves was studied in vitro and in vivo. The extract exhibited trypanocidal activity at all four concentrations tested i.e. 5, 50, 500 and 1000 micrograms/ml, in vitro. In vivo trial revealed that the extract exerted antitrypanosomal effect at dosage of 100, 300 and 1000 mg/kg, intraperitoneally. At 100 and 300 mg/kg doses the survival period of the Trypanosoma evansi infected mice was significantly prolonged. However, the extract was found to be toxic to the animals at 1000 mg/kg dose.