This study investigated a forced convection of nanofluid in a microchannel with the presence of square obstacles using lattice Boltzmann method. The slip boundary conditions for veloc-ity and temperature jump are considered for microchannel. The study is conducted in three volume fractions of nanoparticles, two Knudsen numbers and two Reynolds numbers. The results is shown that with enhancing the volume fraction of nanoparticles, the heat transfer coefficient increases more than two times. It is observed that by increasing the Knudsen num-ber, the velocity slip and also temperature jump increases, but the heat transfer coefficient and the friction coefficient decreases. The first obstacle in the microchannel is more effective which is due to the creation of the vortex and the vortex characteristics in dissembling the hydraulic and thermal boundary layers. Also, increasing the nanoparticles volume fraction, the heat transfer coefficient rises noticeably