Abstract: On the background of the miniaturization of heat exchanger, experimental investigation and analysis of the pressure drop of flow boiling in narrow rectangular channel were conducted. Six correlations for the two-phase friction pressure drop were evaluated against the experimental data. The results show that the correlations for conventional channel poorly predict the results. While the Sun-Mishima and Zhang-Mishima correlations developed for narrow channel are better than other correlations. In the meantime, the constant C in the Chisholm equation for calculating the two-phase friction pressure drop shows the exponential trend against Martinelli parameter X for different mass fluxes. Therefore, a new correlation was developed for calculating the two-phase frictional multiplier and the evaluation shows that it’s better than the other evaluated correlations.