The classical Volmer’s theory of heterogeneous nucleation on solid surfaces was applied to a condensing system of water vapor on n-hexadecane liquid surface. The Volmer’s equation was newly analyzed in the case of liquid surface and an experiment was carried out to study the condensation of water vapor on the surface of n-hexadecane in a thermal diffusion cloud chamber. The observed critical supersaturation was smaller than the theoretical value calculated from the Volmer’s theory. And the critical supersaturation predicted by a kinetic theory was found to be equal to that by the Volmer's equation. The discrepancy of critical supersaturation between experimental and theoretical values probably stemmed from the difference in the value of interfacial tensions between macroscopic and microscopic states. Also this discrepancy seemed to be reasonable since the theoretical and empirical definitions of the critical supersaturation were different.