The high incidence of equine gastrointestinal worms and their increased resistance against anthelmintics has encouraged research into the effectiveness of rational phytotherapy. This study investigates the in vitro anti-parasitic effects of extracts of Ferula asafoetida and Allium sativum, two native plants that are widespread in Iran on Strongylus spp. larvae. Faecal samples were collected from horses, examined by routine parasitology methods and positive samples were used for future examination. After incubation, the third-stage larvae were harvested by the Baermann technique. A hydroalcoholic extract from the plants was used for the antiparasitic study, while tap water was used for controls. Trials for each concentration and control group were performed in three replicates. The results showed that that during the first day of exposure, the hydroalcoholic extract of F. asafoetida at concentration of 10, 50 and 100 mg/ml killed over the 90% of the larvae, and A. sativum extract at concentration of 50 and 100 mg/ml killed over the 95% of larvae (p<0.05). The results obtained from the bioassay showed that two plant extracts have a larvicidal effect on the Strongylus spp. larval stages compared with the control group.