In this paper, immiscible fluid flow in a square microchannel was studied numerically and experimentally, with an emphasis on the slug flow regimes. Accurate calculation of the slug length and slug length distribution plays a crucial role in designing separation facilities quantitatively. The presented work examines how various variables, namely, inlet velocity, channel dimensions, and contact angle, affect slug formation. To accurately track the interface between the water and toluene, the volume of fluid model (VOF) was used to simulate the flow. The inlet velocity of water was varied from 0.02 to 1.28 m/s, while the inlet velocity of toluene was kept constant at 0.08 m/s. From the numerical study, it was observed that the length of the slugs decreases up to 5 times as the water inlet velocity increases. The results are experimentally validated. The effect of wall shear stress and microchannel wettability was observed in slug formation.