Purpose: To investigate the effects of levonorgestrel (LNG), progestin derivative, alone or in combination with melatonin (MEL) on the levels of hepatic reduced (GSH) and oxidised (GSSG) glutathione and malondialdehyde (MDA) which are components of the oxidant-antioxidant system, by using rat as a model. Material and Methods: Female rats were divided into four groups (10 in each) as follows: l-subcutaneous treatment group with LNG (5.0 mg/kg/day) 2-subcutaneous treatment group with MEL (25.0 mg/kg/day) 3-subcutaneous treatment group with a combination of 5.0 mg LNG and 25.0 mg MEL/Kg/day and also a control group: the subcutaneous injections were performed for for five consecutive days. Following the last treatment, the levels of GSH and GSSG and MDA were measured and the ratios of GSH/GSSG calculated in the rat liver tissues. Results: There were no significant differences with respect to GSH or GSSG levels, and GSH/GSSG ratios between the control and MEL groups: but MDA levels were lower in the MEL group. Although GSSG and MDA levels were found to be higher, GSH levels and GSH/GSSG ratio were lower in the LNG group compared with control and the MEL groups. Significant decreased GSSG and MDA levels, but increased GSH levels and GSH/GSSG ratios were observed in the group treated with LNG and MEL combination, in respect to the LNG group. Conclusion: Oxidative damage induced by LNG may be prevented in the presence of MEL: therefore the usage of MEL, as an antioxidant, together with contraceptive steroids may be proposed.