The viscosity of suspensions of rigid spheres is obtained using the model system of hexagonal lattice configuration by means of statistical mechanics. The number of nearest neighbors of a representative sphere in this arrangement is eight which is quite close to the measured coordination number of about seven to eight for randomdly packed spheres. The maximum attainable concentration of the system is 60.4 percent which is comparable with that obtained for the real system of random packing. The viscosity-concentration relationship calculated from the present model is compared with that of earlier work^1） for simple cubic arrangement and found to be in better agreement with the compilations of experimental data of Rutgers and Thomas. It is known from the above analysis that a model dealing with particle configurations is essential to predict the rheological properties of concentrated suspensions.