The diffusion properties of sodium chloride in Grass carp muscle were investigated. A diffusion model based on Fick's second law and Newman expression was presented with the purpose of simulating the salt dynamic distribution in fish fillets. Experimental results indicated that the diffusion properties were greatly dependant on temperature, salt content and muscle orientation. The diffusion coefficients decreased with an increase in brining time but increased with increasing temperature. The diffusion coefficients D(x) and D(y) (normal and parallel to muscle fibers) calculated from the diffusion model ranged from 5.86 x 10(-9) to 3.15 x 10(-10) m(2)/s and from 6.53 x 10(-9) to 4.72 x 10(-10) m(2)/s. The differences in D(x) and D(y) values showed that there existed the anisotropic behavior of salt diffusion in muscle. Activation energy of sodium chloride transfer obtained from the modified Arrhenius model for D(x) (30.54 kJ/mol) was higher than that for D(y) (25.06 kJ/mol), which confirmed that sodium chloride diffusing normal to muscle fibers was more difficult than that parallel to muscle fibers. (C) 2011 Elsevier Ltd. All rights reserved.