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: 411) of ternary solutions (salt-sugar-water) at different initial sucrose (0-100 g in 100 g of water) and salt (0-35.14g in 100 g of water) concentrations at 20degreesC. 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, D-11, 0.91 x 10-(9)m(2)s(-1) and sucrose, D-22, 0.22 x 10(-9)m(2)s(-1), and the calculated cross-term coefficients, D-12 and D-21, were -0.12 x 10(-9) and 0.06 x 10(-9) m(2)s(-1), respectively.