Condensation heat transfer coeffcient and pressure drop of CFC12 and its substitute HFC134a Were measured inside a horizontal smooth tube with an inner diameter of 7.9mm. The mass velocity ranged from 113 to 340kg/(m²s) and the saturation temperature ranged from 40 to 60°C. The local heat transfer coefficient of HFC134a is 10 to 25% higher than that of CFC12 at the same values of saturation temperature, mass velocity, heat flux and vapor quality. The local Nusselt number for both refrigerants is correlated well by an equation which is obtained by modifying a semi-empirical equation proposed by Fujii et al. Experimental results of frictional pressure drop for both refrigerants expressed in the coordinates of Lockhart-Martinelli parameters have the same tendency, while those are lower than the values predicted using previous emprical equations. Judging from the standpoint of condensation heat transfer HFC134a is an appropriate substitute for CFC12.