Mass transfer during osmotic dehydration of watermelon, and colour changes of fresh, osmosed and osmo-oven dried watermelon were investigated. Mass transfer during osmotic dehydration was modeled using Fick's second law of diffusion. CIE colour parameters (L*a*b*) of fresh, osmosed, and osmo-oven dried watermelon were measured and, colour intensity, chroma and hue angle were calculated. Moisture and solid diffusivities were in the range of 1.030x 10(-8)-3.549x10(-9) m(2)/s and 1.117 x 10(-8)-8.540 x 10(-9) m(2)/s, respectively. Activation energy for moisture and solids diffusivity ranged from 5.09 to 32.77 kJ/mol and 3.43 to 32.38 kJ/mol, respectively. Generally, L*. a*. h*. colour intensity and chroma values increased with increase in osmotic solution concentration in osmosed and osmo-oven dried watermelon. (c) 2006 Elsevier Ltd. All rights reserved.