Variation of peroxide value in water-degummed and alkali-refined soy oil during bleaching using regenerated clay under vacuum was investigated in this study. Experimental results indicated that the rate of reduction of dimensionless peroxide value increased with an increase of ratio of clay/oil or bleaching temperature. The rate could also be increased by decreasing bleaching pressure, particle size of clay or water content of clay. Initial peroxide value and agitation speed, however, were found to have no influence on the reduction rate. Furthermore, an empirical relationship between dimensionless peroxide value and bleaching time was determined. Regenerated clay produced in this work was found to be more efficient than activated clay in reducing peroxides. (C) 2007 Elsevier B.V. All rights reserved.