Equilibrated grain boundary groove shapes for solid Sn in equilibrium with Cd-Sn liquid were directly observed after annealing a sample at the eutectic temperature for about 8 days. The thermal conductivities of the solid phase, KS, and the liquid phase, K(L), for the groove shapes were measured. From the observed groove shapes, the Gibbs-Thomson coefficients were obtained with a numerical method, using the measured G, K(S) and K(L) values. The solid-liquid interfacial energy of solid Sn in equilibrium with Cd-Sn liquid was determined from the Gibbs-Thomson equation. The grain boundary energy for solid Sn was also calculated from the observed groove shapes.