In this study heat transfer and fluid flow of a non-Newtonian nanofluid in two dimensional parallel plate microchannel without and with micromixers have been investigated for nanoparticle volume fractions of phi = 0, phi = 0.04 and nanofluid Reynolds numbers of Re-nf = 5, 20, 50. The nanofluid is composed of CuO nanoparticles and the non-Newtonian base fluid of 0.5 wt% aqueous solution of Carboxymethyl Cellulose (CMC). Two baffles on the bottom and top walls work as micromixer. A single-phase finite difference FORTRAN code using Projection method has been written to solve the governing equations with constant wall temperature boundary condition. A new correlation for thermal conductivity of this nanofluid has been introduced and also the effect of various parameters such as the baffles distance, height and order of arranging has been studied. Results show that the presence of baffles and also increasing the Re number and nanoparticle volume fraction increases the local and average heat transfer and friction coefficients of non-Newtonian nanofluid. Also, the effect of nanoparticle volume fraction on heat transfer coefficient is more than friction coefficient in most of the cases. It was found that the main mechanism of enhancing heat transfer or mixing is the recirculation zones that are created behind the baffles. The size of these zones increases with Re number and baffle height. The fluid pushing toward the wall by the opposed wall baffle and reattaching of separated flow are the locations of local maximum heat transfer and friction coefficients. (c) 2014 Elsevier Ltd. All rights reserved.