The study on osmotic dehydration of onion slices was carried out in order to remove the moisture prior to the further mechanical drying. Three salt concentration levels (5%, 12.5% and 20%), three temperature levels of osmotic solution (28 degrees C, 43 degrees C and 58 degrees C) and the observations on weight loss and solid gain were taken at an interval of 5 min up to first half an hour followed by interval of 10 min for next 1 h. The sample to solution ratio of 1:5, agitation of 100 shakes per minute, sample thickness of 4 mm and 0.2% potassium metabisulphite mixed with osmotic solution were used for the study. A two-parameter mathematical model developed by Azuara et al. was used for describing the mass transfer in osmotic dehydration of onions slices. The effect of time on mass transfer kinetics was investigated and the constants of two-parameter model and final equilibrium points for moisture loss as well as solid gain were found. The effect of solution concentration and solution temperature was also studied and it was found that equilibrium moisture loss and solid gain are related to solution concentration and solution temperature logarithmically. The optimum conditions of osmotic dehydration for further drying were found to be 20% salt concentration, 28 degrees C solution temperature and 1-h of osmosis. (c) 2005 Elsevier Ltd. All rights reserved.