Background: Production of anti-Toxoplasma drug with high efficacy and low side effect is one of the main priorities in toxoplasmosis researches. Herbal extracts has considered as a candidate for this purpose.

Objective: This study was performed in order to determine lethal effect of Artemisia absinthium L., Carum copticum L. and Gossypium hirsutum extracts on Toxoplasma gondii tachyzoites in vitro free cell line.

Methods: Tachyzoites of T. gondii RH strain were treated with concentrations of 10, 50, 100, and 200 mg/ml of Artemisia absinthium L., Carum copticum L., and Gossypium hirsutum extracts within 10, 30, and 45 min. Afterward, the tachyzoites were stained with alkaline methylene blue. Mortality rates of tachyzoites treated with extracts were determined. The results were analyzed with one way ANOVA and Post Hoc Test by SPSS software. P<0.05 was considered to be statistically significant.

Results: The overall, 100% of tachyzoites were killed at concentrations of 50, 100, and 200 mg/ml of Artemisia absinthium L. and 200 mg/ml of Carum copticum L. after 10, 30, and 45 min treatment. The lowest mortality rates at concentration of 10 mg/ml were 19.6±8.4, 4.30±2.26, and 4.63±2.1 for Artemisia absinthium L., Carum copticum L., and Gossypium hirsutum, respectively. The highest and lowest mortality rate of tachyzoites by Gossypium hirsutumin extract was
13.3 ±7.1. The mortality of tachyzoites were confirmed by bioassay in mice.

Conclusion: Anti-Toxoplasma activities of Artemisia absinthium L. and Carum copticum L. were significantly higher than Gossypium hirsutum. Further studies in order to clarify effectors are recommended.