The rapid development of microfabrication techniques creates new opportunities for applications of microchannel reactor technology in chemical reaction engineering. Because of large surface to volume ratios and small traort paths in two phase microchannels flow, mass and heat transfer is high. Hence use of microchannels is increasing. The extremely large surface-to-volume ratio and the short traort path in microchannels enhance heat and mass transfer dramatically, and hence provide many potential opportunities in chemical process development and intensification. Multiphase reactions involving gas and liquid reactants with a solid as a catalyst are ubiquitous in chemical and pharmaceutical industries. For gas and liquid two-phase flow in a microchannel, the Taylor slug flow regime is the most commonly encountered flow pattern. The performance of microchannels largely depends on the underlying hydrodynamics of the gas and liquid flow. Thentostudy the flow and traort phenomena in microchannels must first hydrodynamic behavior be determined. In this work, we study the hydrodynamic behavior of a Taylor slug gas and liquid system in flow microchannels using Computational Fluid Dynamics(CFD). A T-junction empty microchannel with varying cross-sectional width (0.25, 0.5, 0.75, 1mm) served as the model micro-reactor, and a finite volume based commercial Computational Fluid Dynamics (CFD) package, FLUENT, was adapted for the numerical simulation. The two-phase pressure drop and the lengths of gas and liquid slug with 1%-AL 2 O 3 /water Nano fluid-air as the working fluid at various operation and fluid conditions were obtained and found to be in good agreement with the literature data. Simulation result show that the volume of fluid in both 2D as well as 3D, predict pressure and the values obtained, are in good agreement with theoretical Young-Laplace pressure and previous articles. Surface tension is the most dominant role in determining the pressure drop and slug properties in microchannels and the Bond number appropriate criterion the effects of gravity. The length-averaged friction factor for the liquid slug increased four times from the single phase value (f.Re=16). The dimensionless slug length is mainly determined by the phase hold-up, with a slight effect of Re and Ca. Therefore, wider channels have longer slug length at the same superficial gas and liquid velocities. Gravitational effects can be ignored in microchannels. The gas slug length increases with increase in superficial gas velocity, and decrease in superficial liquid velocity. The liquid slug length increases with increase of liquid velocity, and decrease of superficial gas velocity.