In this study, two new correlations are developed to predict pressure drop for the flow boiling in micro systems with low mass flux. The correlations developed rely on extensive experimental results. Experiments are conducted for flow boiling in nine different silicon multichannel heat sinks with deionized water. In the experiments, mass fluxes of 51-324 kg.m(-2).s(-1), wall heat fluxes of 36-121.8 kW.m(-2), exit vapor qualities of 0.04-0.81, liquid-only Reynolds number of 20.3-89.4, aspect ratios of 0.37-5.00 and hydraulic diameters of 100-250 mu m are tested. At first, validation tests for the single phase have been conducted. Then, some of the well-known existing correlations developed for the prediction of two phase pressure drop are used for comparison of the experimental results obtained. Finally, two new empirical correlations are developed for low mass flux conditions. The first one is for frictional pressure drop component, which is obtained by following a general procedure. The second one is for the prediction of total pressure drop (a dimensionless pressure drop correlation). The latter has been shown to predict better with an overall mean absolute error of 14.5% and, 87.8%, 94.8% and 96.5% of the predictions falling within +/- 30, +/- 40 and +/- 50% error bands, respectively.