A group contribution method is developed on the basis of the UNIDIF model [Y.D. Hsu, Y.P. Chen, Fluid Phase Equilibria 152 (1998) 149-168] for the correlation of the mutual diffusion coefficients of binary liquid mixtures. In this group contribution UNIDIF (GC-UNIDIF) model, a mole fraction average of the logarithm of the infinite dilution limiting diffusion coefficients is taken as a reference term. The model expresses the excess part of the diffusion coefficient relative to this reference term in a form similar to that of a UNIFAC equation with two parts due to the combinatorial and residual contributions. The combinatorial part depends on the molecular sizes and shapes. The residual part includes two binary interaction parameters, which are obtained from generalized data regression, for each pair of functional groups. Optimal group interaction parameters are presented. The mutual diffusion coefficients of binary liquid mixtures are calculated for non-polar+non-polar, non-polar+polar and polar+polar fluid mixtures in this study. The calculation results using the GC-UNIDIF model for mutual diffusion coefficient are satisfactory. This model also requires lesser number of parameters than other correlative methods.