Gastrointestinal nematode infections in ruminants have direct effects such as mortality, weaknesses, feeding efficiency and decreased productivity. Animal deaths due to nematode infections are common in tropical regions where control programs based solely on the use of synthetic anthelmintics are no longer sustainable due to increased prevalence of gastrointestinal nematode resistance, slow development of new anthelmintics, high costs to poor farmers and concerns regarding residue in food and the environment. Alternative methods of control are thus required. Prosopis juliflora is a fast-growing, drought-resistant tree adapted to poor and saline soils in arid and semi-arid lands of Kenya, inhabited by nomadic pastoralists. Analysis of the EHA data using t- test revealed that there was no statistically significant difference in the activities of both LEE and REE (p>0.05). However, in comparison to ALB, the difference in activity was significantly different (p<0.05). The observed in vitro anthelmintic activity was attributed to saponins and condensed tannins and to alkaloids present in the plant. Phytochemical analysis confirmed presence of tannins, saponins and alkaloids, among other phytoconstituents. These phytochemicals are known to exhibit anthelmintic activity, therefore making the plant a potential candidate for drug development against gastrointestinal nematodes.