Microfluidic systems (lab-on-a-chip devices) are widely employed in micro-technology areas such as biology, medicine, chemistry, chemical engineering and biotechnology; applications varies from protein and DNA analysis, high-throughput screening, autonomic materials, sensors, chemical reactions, small quantities transfer (1÷100 nl) of fluids, fluidic-based computers, micro electronics mechanical systems (MEMS). These systems are preferably to operate in a pressure driven flow regime with no moving parts. Our research is aimed at rigorous assessment and quantification of mixing in microchannels. The work presented is based on numerical simulations of flow in different geometries coupled with mixing assessment using entropic measures. The results show enhanced mixing efficiency for the geometry similar to the staggered herringbone mixer by comparison with a mixer with straight diagonal ridges and lack of mixing in a non-patterned channel. These results are in agreement with published experimental data.