Understanding the flow fields at the micro-scale is key to developing methods of success-fully mixing fluids for micro-scale applications. This paper investigates flow characteristics and mixing efficiency of three different geometries in micro-channels. The geometries of these channels were rectangular with a dimension of; 300 m wide, 100 m deep and 50 mm long. In first channel there was no obstacle and in the second channel there were rectangular blocks of dimension 300 m long and 150 m wide are placed in the flow fields with every 300 m distance attaching along the channel wall. In the third geometry, there were 100 m wide fins with 150° angle which were placed at a distance of 500 m apart from each other attached with the wall along the 50 mm channel. Fluent software of Com-putational Fluid Dynamics (CFD) was used to investigate the flow characteristics within these microfluidic model for three different geometries. A species 2D model was created for three geometries and simulations were run in order to investigate the mixing behaviour of two different fluid with viscosity of water (1 mPa s). Models were only built to investigate the effect of geometry, therefore only one fluid with similar viscosity was used in these models. Velocity vector plots were used in the CFD analysis to visualise the fluid flow path. Mass fractions of fluid were used to analyse the mixing efficiency. Two different col-ours for water were used to simulate the effect of two different fluids. The results showed that the mixing behaviour strongly depended on the channel geometry when other parameters such as fluid inlet velocity, viscosity and pressure of fluids were kept constant. In two geometries lateral pressure and swirling vortexes were developed which provided better mixing results. Creation of swirling vortexes increased diffusion gradients which enhanced diffusive mixing.