In vitro, the anthelmintic activity of Cassia fistula was studied on the pathogenic liver fluke Fasciola gigantica. Live liver flukes were collected from the infected part of the liver and bile duct of the freshly slaughtered domestic goat at the local meat market of Udaipur, India. The in vitro anthelmintic efficacy of aqueous and alcoholic extracts of Cassia fistula leaves at different concentrations of 10, 20, 30, 40, and 50 mg/ml for 2 to 10 h of exposure time were evaluated against the pathogenic liver fluke F. gigantica. The study revealed that alcoholic and aqueous extracts of C. fistula caused more mortality compared to albendazole. The alcoholic extract was more potent than the aqueous extract of C. fistula. The present research work is of significance because it would help to prepare less costly, eco-friendly, anthelmintic, and veterinary herbal drugs to replace the synthetic drugs that are currently in use.