Objectives : The aim of this study was to develop a more simple and convenient manufacturing method of Rehmanniae radix Preparata without benzopyrene content than the traditional 9-times steaming process. Methods : The Rehmanniae radix was steammed to various times at 120℃ under high pressure. The contents of benzopyrene which was known as a tumor promoting agent were analysed. Also, the contents of 5-hydroxymethyl-2-furaldehyde (5-HMF) which was known as standard compound in Rehmanniae radix Preparata were analysed. The antioxidant activities of Rehmanniae radix Preparata were evaluated for radical scavenging activity against stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitrite radical, and superoxide anion radical. In addition the antioxidant activities of Rehmanniae radix Preparata against peroxyl radicals and hydroxyl radicals were determined by the total oxy-radical scavenging capacity (TOSC) assay. Results : The contents of benzopyrene and 5-HMF were gradually increased with increasing steaming time at 120℃ under high pressure. Moreover, the antioxidant activities of Rehmanniae radix Preparata were increased with increasing steaming times. Conclusions : Based on the present results, it can be suggested that the 2-4 hr steaming at 120℃ under high pressure is the most optimal processing condition and Rehmanniae radix Preparata can be useful to develop functional food against oxidative stress conditions.