Conjugate heat transfer method is utilized in this work for numerically studying the laminar two-dimensional forced convective heat transfers related to the aluminum oxide-water nano-fluid in horizontal micro wavy channel also the impact of adding nano-particles for constant heat flux applied at bottom the channel, The study assumed that the nanofluid is subject to the single phasic hypothesis that treats the basic fluid (H2O) and nanoparticles (Al2O3) as a homogeneous mixture and that the nano-fluid is incompressible and it has steady and laminar flow. The considered Reynold number and the nano particle volume fraction have been in a range between (500 and 2,000) and 2% respectively. Use the (ANSYS FLUENT 2020 R1)software, which is one of the programs regarding the computational fluid dynamics (CFD), and Finite volume method (FVM) is selected to solve the governing equations For ensuring the accuracy of results, the CFD result were verified with modern theoretical equation. In this research four models are examined numerically, The first model is a flat channel and only water is flowing through it, The second model is a wavy channel and only water is flowing through it, The third model is a flat channel where the nanofluid consisting of water and nanoparticles (aluminum oxide) passe through it, and the fourth model is a wavy channel in which the nanofluid consisting of water and the nanoparticles ( AL2O3) passes through the channel for three different values of Reynolds number (500,1400,2000) and concentration of (2%) nanoparticles. A micro-wavy channel represents an optimal state among all examined cases and with regard to all the Reynolds numbers. Furthermore, the best Performance evaluation criterion (PEC) is recorded for the case of wavy channel with nanofluid for Reynolds number equaling 2000. At Re = 2000 with 2% as volume concentration, the value related to heat transfer coefficient equal to (4603.61) when using the nanofluid due to dispersion factors, Brownian motion, and nanoparticles that are responsible for enhancing heat transfer. The presence of wavy channel and nanofluid flow enhance the nusselt number and improve heat transfer to fluid. It is noticed that when Reynolds number increases the pressure drop increases, the thermal resistance decreases, the heat transfer coefficient increases. The addition of waves in the channel and nanoparticles increased the number of Nusselt and thus improved heat transfer.