Two dimensional analysis of fluid flow and heat transfer through the trapezoidal microchannel has been done. The energy and Nervier stokes equations have been solved considering the wall slip velocity and temperature jump using the Lattice Boltzmann method (LBM). The relation between relaxation times and Knudsen number has been derive in LBM. The effects of Reynolds number, Nusslelt number, temperature jump and velocity slip on different Knudsen number (0.001<Kn<0.1) and different aspect ratios (0.2<AR<1.2) were investigated. The good agreement between results and earlier studies were found. Results show the important effect of AR and Knudsen number on Nusselt number in trapezoidal microchannel. At low Reynolds number the significant influence on Nusselt number has been seen. Manuscript profile