Objective: Galbanic acid is a sesquiterpene coumarin from some species of the genus Ferula Galbanic acid was separated from the roots of Ferula szowitsiana using silica gel column chromatogeraphy, followed by preparative thin layer chromatogeraphy. In the present study, the protective effect of galbanic acid isolated from Ferula szowitsiana on DNA damage in healthy human lymphocytes induced by H2O2 was evaluated using single-cell electrophoresis (Comet assay). Materials and Methods: Effect of Galbanic acid at concentrations of 200 and 400 μM , in the presence of concentrations of 25, 50, 100 and 200 μM of H2O2 was tested on lymphocytes derived from the blood of healthy volunteer were measured by comet assay. The degree of damage to DNA after exposure to different solutions at 4° for 15 minutes was calculated based the amount of DNA present in the tail compared to the total amounts of lymphocyte DNA. Results: No toxicity was found in Galbanic acid against human lymphocytes. Galbanic acid did not cause DNA damage at concentrations of 200 and 400 μM as compared with a control group. When galbanic acid at concentrations of 200 and 400 μM, was mixed with H2O2 25 µM for reaction, it didn’t exhibit inhibitory effect on DNA damage induced by H2O2. Conclusion: Galbanic acid did not cause DNA damage at concentrations of 200 and 400 μM as compared with a control group.