Since the demand of plasticizers is increasing and limiting amount of petroleum, rice bran oil (RBO) can be used as an alternative raw material to produced epoxidized oil. Epoxidized rice bran oil (ERBO) can be used as plasticizers & stabilizers of polymers. This research is aimed to investigate the effect of reaction period and temperature of epoxidation reaction on the reaction conversion and oxirane content of epoxidized oil product and to achieve optimum operating condition indicated by high content of oxirane groups. Response surface methodology was performed to determine the optimum operating condition in the epoxidation of rice bran oil. Epoxidation reaction was run in a batch reactor using acetic acid as an oxygen carrier. Central composite design, with two variables and two response functions was used to learn the influence of input variables on the response variables. The result showed that the conversion of iodine value in the RBO increases linearly with the increase of reaction period and temperature. The optimum condition indicated by high percentage of oxirane oxygen content was achieved at reaction period of 4.3-h and temperature of 63.8oC.