In this study, water activity, moisture content reduction and solute uptake kinetics as well as mass transfer in osmotic dehydration of tilapia (Oreochromis niloticus) fillets were studied, using limited volumes (solution/fillet ratio: 4/1) of ternary solutions (salt-sugar-water) at different initial sucrose (0-100 g in 100 g of water) and salt (0-35.14 g in 100 g of water) concentrations at 20°C. The multicomponent effective diffusion coefficients were calculated by fitting the experimental values to analytical solution of mass transfer equations with a limited solution/fillet ratio. Previously, the effective diffusion coefficients of salt and sugar in tilapia muscle were calculated using a binary system. A very good fit between the mathematical model and experimental values was observed. The binary coefficients obtained were: for sodium chloride, D11, 0.91 × 10-9m2s-1 and sucrose, D22, 0.22 × 10-9m2s-1, and the calculated cross-term coefficients, D12 and D21, were -0.12 × 10-9 and 0.06 × 10-9m2s-1, respectively. © 2002 Elsevier Science B.V. All rights reserved.