: Nowadays with development of technology, the production and utilization of micromixers in different dimensions has considerably grown, especially in medical and biochemistry industries. Due to production problems and costs in such a dimension, simulation and optimization of the micromixers before production and experiment, is crucial. The only mechanism for mixing species in micro dimension is the mass diffusion phenomena, since the Reynolds number is low and the flow is laminar. Small mass diffusion coefficient of biological species prevents achieving desirable results by this mechanism. In order to accelerate the mixing process and obtain a homogeneous mixture of samples, various schemes have been presented so far. In this work, two different mechanism are considered to enhance the performance of micromixer. First, it was tried to use acoustic waves and streaming for improving the mixing of two fluids with low Reynolds number. Perturbation analysis method is used to model the impact of acoustic waves on fluid. Unfortunately, in spite of our best endeavors, the problem was not completely solvable with this method. In the second approach, oscillatory inlet velocities are used in order to enhance mixing in micromixer. In this approach, the impact of parameters’ variation and various dimensionless numbers on efficiency (mixing degree), is investigated. These parameters and dimensionless numbers are: Strouhal number, pulse amplitude to base velocity ratio, Reynolds number, location along the mixing channel normalized by the channel width and phase difference between the inlet streams. Results show that the mixing efficiency along the channel suffers from locational fluctuations. Mixing degree locational fluctuations are the lowest in phase angle offor different Strouhal numbers. In addition, variation of pulsation amplitude and frequency has the most influence on mixing degree improvement. For certain and , in specified Strouhal number, the mixing degree reaches to its maximum value, while for other values of Strouhal numbers the efficiency decreases. For example, for the optimum Strouhal number is 2 and the mixing efficiency is 0.79 for the length of equivalent to ten times of channel width, which is an acceptable value. The increase of pulsation amplitude to base velocity ratio always improves mixing degree. Moreover, the mixing efficiency averaged over a cycle in quasi-stationary state increases by moving along the mixing channel. The best state for input streams is choosing phase difference of for input velocities, since the maximum mixing degree is obtained in this phase angle. Furthermore, in order to avoid the variation of other dimensionless numbers, Reynolds number is varied just by variation of fluid dynamic viscosity from 0.2 to 200. Results show trivial impact of Reynolds number variation on mixing efficiency. This occurs because velocity profiles vary by Reynolds number variation in the mixing channel, while average velocity remains fixed. Subsequently, Peclet number does not vary and is fixed for all Reynolds numbers. Keywords: Active micromixer, Acoustic Waves, Streaming, Oscillatory Velocities, Strouhal, Mixing degree