In this study, the mixed convective heat transfer in a lid driven square cavity at different inclination angles is investigated numerically using lattice Boltzmann method with Boussinesq approximation. The vertical walls of the cavity are insulated, while the bottom (hot wall) and top (cold lid) surface are maintained at a uniform temperature. The study is carried out forRichardson numbers ranging from 0.01 to 10 and an inclination angle of cavity ranging from 90 to 90. TheseRichardson numbers are selected based on the inclusion of forced, mixed and natural effects. The result shows that the heat transfer rate is independent of the inclination angle for Ri of 0.01, whereas it changes when theRichardson number increases. Moreover, it has been found that this effect is positive for negative angles and negative for positive angles that are due to the effect of buoyancy force on flow field. In addition, the verity of Nusselt number andRichardson number are opposite because the natural convection changes to mixed or forced convection when theRichardsonnumber decreases. Consequently the Nusselt number increases.