The performance of different micro-mixers has been examined experimentally and by the use of computational fluid dynamics (CFD). The development and occurance of turbulence is very important for good mixing quality in the micro-mixers that were examined. Due to the small diameter of the microchannels the batchelor length is reached much faster and there are less inhomogenities in concentration so that side reactions are reduced effectively. Furthermore, it could be shown that the mixing performance of micro-mixers could be simulated in good agreement with the experimental results using existing turbulence models. On the basis of CFD the influence of the geometrical parameters of the micro-mixers were investigated. These results show that the mixing behavior is mainly influenced by the channel height and direction.