The objective of this study is to evaluate the efficacy of Artemisia herba alba oil extract and its nano-emulsion in treatment of artificially infected lambs by Trichostrongylids. A total of 15 lambs were allocated into five groups. On 0 day, the animals of the first four groups were inoculated with 3000 Trichostrongylids L3 and 5th group were left as control negative. On the 2nd DPI, G1, G2 and G3 were treated with 100 mg/kg b. w. A. herba alba oil extract, 100 mg/kg b. w. of A. herba alba nano-emulsion and 7.5 mg/kg b. w. albendazole respectively. Animals of group 4 were kept as control positive group. The shedding of eggs began from 15th day in G1 and G4 only. There was significant decrease (P