Systematic molecular dynamics simulations have been performed to illustrate the roles of guest molecules played in the process of hydrate growth at vapor-liquid interfaces. In our simulations, guest molecules are represented by a commonly used single-site Lennard-Jones model, and the roles of guest molecules on hydrate growth have been investigated separately from the effect of water-guest molecule attractive interaction epsilon and that of molecular size sigma, respectively. Our simulation results demonstrate that the water-guest molecule attraction regulates the pathway and rate of nucleus growth, whereas the size of guest molecules determines the dynamically preferable structure. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 2621-2629, 2013