Stachytarpheta jamaicensis L. Vahl has traditionally been used as an anti-trematode, but its effectiveness needs to be scientifically tested. This study aimed to determine the anti-trematode activity of the Stachytarpheta leaf extract in vitro. The leaves were extracted using water, and their secondary metabolites were characterized by phytochemical screening. Paramphistomum sp isolated from the rumen was identified by morphometric determination. In vitro analysis of anti-trematode activity was carried out by post-test design, with control groups consisting of positive control (10% Albendazole) and negative control (0.9% NaCl), and the treatment groups consisting of the leaves aqueous extract with various concentrations (2.5%, 5%,10%). The anti-trematode effect was determined by the time required to destroy the worms. The results of phytochemical screening showed that the secondary metabolites contained in the extract were alkaloids, flavonoids, tannins, steroids, and triterpenoids. The average time of worm death was 30 and 240 minutes for positive and negative controls. In comparison, the extract with concentrations of 10%, 5%, and 2.5% killed the Paramphistomum in an average period of 45, 60, and 80 minutes. Amongst the treatment groups, the extract at 10% concentration was the most effective (p<0.05), indicating its potential use as an anti-trematode.