AbstractBackground:Visceral leishmaniasis (VL) is a parasitic disease that affects public health. It is described by weight reduction, irregular fever bouts, anemia, and amplification of the spleen and liver.Materials and Methods:Three concentrations (15.6, 31.2, and 62.5 μg/mL) were used to find the potency of an aqueous extract ofChara vulgarisalgae in the treatment of VL. A cytotoxicity assay was performed to show the cytotoxic effect of this extract on human cells. High-performance liquid chromatography (HPLC) test was done to determine the active compounds in the extract. Histopathological sections for infected liver and spleen were performed, as were liver function tests (alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase), which were assessed after 1 month of treatment.Results:As cytotoxicity assay, results showed that there were no significant differences between the cells treated and those not treated with the extract. HPLC test demonstrated that phenolic and terpene compounds are the main active compounds in the extract. P-coumaric acid and ursolic acid present the highest percent among other phenolic and terpene compounds (21.84%, 17.82%), respectively. Histopathological sections showed that this extract had a significant effect in the treatment of infected tissues, and this effect was very clear after the end of the treatment period. As for the liver function tests, a significant increase (P< 0.01) in the studied liver enzymes was found in the infected group of mice compared to the healthy group, whereas in the infected and treated groups, a clear and gradual decrease in the level of enzymes was observed.