Experiments are carried out for passive mixing in order to obtain local mean and turbulent velocities and concentrations. The mixing takes place in a square channel with two inlets separated by a block. A combined PIV/PLIF technique is used to obtain instantaneous velocity and concentration fields. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k -turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between the measured and predicted mean and fluctuating concentrations. The multi-peak presumed PDF mixing model is tested and comparisons with experiments are encouraging.KEYWORDS: mixing, PIV, PLIF, CFD, mass transfer, probability density function * The following foundations are acknowledged for their financial support to the laser laboratory at Aalborg University Esbjerg: Lida og Oscar Nielsens fond, Fabrikant Mads Clausens fond, Esbjerg seminarie fond, Direktør Ib Henriksens fond, Fabrikant P.A. Fiskers fond, Obelske fond and DONG's jubileumslegat.