Microreaction engineering enables new strategies in process intensification. A precise analysis of local mass transfer and hydrodynamics in micromixers for different flow regimes are strongly needed for a complete understanding the processes occurring. One of the simplest in the manufacture, but at the same time, quite effective T-shaped micromixer was used for numerical investigation and analyzing the mixing quality and flow regimes as well as the influence of different fluids properties on this parameters. It was numerically revealed that the viscosities and the densities, as well as the initial temperatures and the rheology of mixing fluids have significant effects on the flow regimes and the mixing efficiency of two fluids. In this study viscosities and densities ratios of mixing fluids ranged from 1 to 2; the coefficient n in power-law model of non-Newtonian fluids ranged from 0.3 to 1; the initial temperatures difference of two fluids was varied up to 40 degrees C. Mixture components concentration as well as pressure and velocity fields distribution in the micromixer was obtained. The dependence of fluids mixing efficiency and the pressure drop, as well as a map of flow regimes and mixing modes on the Reynolds number and properties of miscible fluids was numerically established.