Solid-liquid equilibrium for binary mixtures of phenanthrene-biphenyl has been obtained by thaw-melt method. The mechanism of eutectic solidification of this binary system has been investigated by spontaneous crystallisation, linear velocity of crystallisation and viscosity determination. Excess molar volume, excess viscosity, free-energy of activation for now, and Grunberg Nissan parameter d have been calculated. The diffusion process has been found to be the dominant factor in explaining the decrease in the unidirectional velocity of crystallisation as one component is added to the other and also explains the higher growth rate for the eutectic mixture.