free-living amoeba, this parasite has a very high lethality, especially in people with underlying diseases, so researchers are always looking for a way to combat it. Drug plants are a good way to fight Acanthamoeba species. In this study, we aimed to investigate the lethal effect of the extract of Oliveria decumbens vent and Peganum harmala alcoholic extract on Acanthamoeba. Methods & Materials In this study using the extract from an extract of Oliveria decumbens vent and Peganum harmala with concentrations of 1. 25, 2. 5, 5, 10, and 20 mg/ml to investigate the lethal effect of this extract. The plant was treated with Acanthamoeba amoebae after three times (24, 48, and 72) hours. Ethical Considerations This study was approved by the Ethics Committee of the Jahrom University of Medical Sciences (Code: IR. JUMS. REC. 1398. 029). Results The present research showed that using different concentrations at three times (24, 48, and 72) hours the effect of the extract on trophozoites and cysts of Acanthamoeba was shown. The highest lethality is related to the concentration of 20 mg/ml using a combination of both extracts at the time 72 hours and the lowest lethality is related to the concentration of 1. 25 mg/ml of Oliveria decumbens vent at the time 24 hours. Conclusion Observations indicate that the alcoholic extract of Oliveria decumbens vent and Peganum harmala had a perfect effect both separately and in a combination of both extracts. These two extracts had a synergistic effect on the lethal effect of Acanthamoeba amoeba.