Objective: To evaluate the in vitro and in vivo efficacy of quercetin and its immunomodulatory and anti-oxidative activity against Leishmania major (L. major). Methods: L. major promastigotes and amastigotes were incubated with different concentrations of quercetin to estimate EC50. For in vivo study, the base of tails of mice was infected with L. major. After developing ulcers in the inoculation site, mice were treated with 50 mg/kg quercetin orally for 28 consecutive days. The wound-healing potential of quercetin was evaluated by histopathological analysis of tissue sections stained by hematoxylin and eosin as well as Masson's trichrome. In addition, the levels of tumor necrosis factor-α, interleukin-6, malondialdehyde, and adiponectin, the ferric reducing ability of plasma, as well as superoxide dismutase and glutathione peroxidase activities were measured. Results: The EC50 values of quercetin against L. major promastigotes and intracellular amastigotes were 0.27 and 0.85 μM, respectively. Histopathological analysis showed that fewer inflammatory cells, more fibroblasts, and more collagen deposition were observed in tissue sections of quercetin-treated mice. In addition, treatment with quercetin markedly increased glutathione peroxidase activity, the ferric reducing ability of plasma and adiponectin levels while decreasing malondialdehyde, interleukin-6, and tumor necrosis factor-α levels. Conclusions: Quercetin shows anti-leishmanial activity, immunomodulatory, anti-oxidative, and anti-inflammatory effects. Therefore, it may be further explored as an effective drug in treating leishmaniasis.