Microchannels have been widely used by the refrigeration/air conditioning industry. Zhao et al. (2000a,b) presented their experimental results for CO2 flow boiling in microchannels. In the present study, empirical modeling is performed to correlate the experimental data. Five state-of-the-art, large-tube empirical models are compared with the experimental data. It is found that these correlations fail to satisfactorily predict the experimental data for microchannels. This indicates that the heat transfer behavior in microchannels is different from that in large channels. A new correlation is developed based on Liu and Winterton’s correlation by introducing confinement factor to account for the micro-scale effects. The new model agrees well with the experimental results for CO2 flow boiling in microchannels within ±20%.