Natural convection characteristics of Al 2 O 3 -water nanofluid in a cavity is investigated numerically under the influence of a inclined magnetic field. The bottom wall is partially heated, and the top wall is cooled and the remaining regions of the cavity are kept adiabatic. An isothermally heated square blockage of the different rectangular size is placed at the centre of the cavity. The schematic model is converted into mathematical form, and the non-dimensional equations are discretized by the finite volume method using power law scheme and solved by Semi-Implicit Method for Pressure Linked Equation algorithm. The relevant parameters such as Rayleigh number (10 4 -10 6 ), Hartmann number (10-500), size of blockage ratio (0.25-0.75), length of the heat source (0.25-1.0) and inclination angle of the magnetic field (0 • -90 • ) on the flow and temperature fields are examined. Results are presented in terms of streamlines, isotherms, velocity profile, local and average Nusselt number. It was found that for low Hartmann numbers, the average heat transfer rate attained the maximum at the inclined magnetic field of γ = 45 • . In addition, the blockage ratio of B = 0.75 enhanced the higher heat transfer rate for all values of γ.