Condensation heat transfer in a vertical tube has been investigated analytically by considering the vapor flow and mass transfer. Condensation processes are divided into two sections: the forming film section and the formed film section. The present analysis takes into account the effects of momentum transfer that results from mass transfer and vapor flow on the interfacial shear and hence condensation. Two major parameters that govern the condensation heat transfer the relative velocity ratio B and the momentum transfer factor U, along with a comprehensive factor w that includes mass transfer, the vapor velocity and the thermophysical properties, are proposed to describe the condensation mechanism. It is shown that the effects of interfacial shear and mass transfer are strongly dependent on the thermophysical properties of the working fluids and the operating temperatures. The theoretical predictions are in good agreement with the experimental data from other investigations for the upward vapor flow in water cases.