The mutual diffusion coefficients Of L-proline, L-threonine and L-arginine in aqueous solution at 25 degreesC were determined by the metallic diaphragm cell method, which is characterized by accuracy, promptness and convenience. The viscosity of these solutions was also determined. Based on these data, a semi-empirical model for correlating the diffusion coefficients of amino acids in their aqueous solutions at 25 degreesC was developed. The model was compared with literature data. Results showed that this model provides significant improvement in correlation of diffusion coefficients for many systems as compared with the original Gordon model. a semi-empirical model.