A theoretical derivation of condensation coefficient based on transition state theory is presented in this paper by considering the three-dimensional movement of condensing molecules in the liquid-vapor interface region. The theoretical expression is a function of free volume ratio of liquid to vapor and activation energy for condensation. We have developed an evaluation of the activated state conditions in the interface region with the use of molecular dynamics (MD) simulations for argon and water. From the molecular scale consideration, it is found that a characteristic length ratio (3)rootV(l)/V-g has an important role in evaluating the condensation coefficient because the restricted translational motion is dominant in the condensation process compared with the rotational motion. Present theoretical values agree well with MD results in both monatomic and polyatomic polar molecules. Finally, we conclude that the condensation coefficient is an inherent physical property of a given pure liquid-vapor interface and the interface structure plays a primary role in condensation. (C) 2003 American Institute of Physics.