A new model is developed for predicting the transition from the slug to annular¯ow of adiabatic two-phase gas/liquid¯ow in microgravity (mg) environment. This model is based on the analyses of the eects of the surface tension and the gas inertia in a sense of more physical approach. The drift-¯ux model is applied to determine the gas void fraction near the transition region. The new model is compared with previous models and experimental data, and the results show the improvement in explanation of the experimental results.