An analytical modeling of condensation heat transfer characteristics under reflux cooling mode inside vertical tubes surrounded by isothermal external fluid was conducted in the present work. The dimensionless film thickness, film Reynolds number as well as the heat transfer coefficient in the condensate film were formulated and calculated numerically. The results indicate that the increase in Blot number thickens the film layer, speeds the film Reynolds number, and increases the condensation heat transfer coefficient. As Bi much greater than 1 and (N) over cap u = 1, the limiting cases for both isothermal wall and uniform wall heat flux, respectively, were derived for comparison. As compared with the experimental data of reflux condensation from previous studies, the analytical results show good agreement with the observed trend of the condensation heat transfer. (C) 1999 Elsevier Science Ltd. All rights reserved.