A detonation wave propagation along a two-dimensional 1-mm-width channel in hydrogenoxygen stoichiometric mixture has been simulated by Direct Simulation Monte Carlo method. A detailed chemical kinetic mechanism for 6 species has been implemented and all the chemical reactions have been modeled at a level of molecular collisions. Unsupported Chapman-Jouguet detonation has been observed with condition of specular reflection of molecules on the side walls. When friction and heat conduction on the side walls are taken into account through diffuse reflection conditions a detonation wave is significantly weaker and its propagation velocity is lower than predicted by the Chapman-Jouguet theory.