Natural convection of micropolar fluid in a square cavity with uniform and nonuniform heated thin plate built in horizontally or vertically is investigated numerically. The non-uniform heating is due to the non linearly varying temperature of the plate. The vertical walls are cooled while the top and bottom walls are insulated. The flow with in the cavity is assumed to be two dimensional. The governing equations were solved by finite volume method using second order central difference scheme and upwind differencing scheme. The computational results are presented in the form of isotherms, streamlines and average Nusselt numbers. The study was performed for different Rayleigh numbers, Prandtl numbers, length of the heat source, location of the plate, vortex viscosity parameter and source non-uniformity parameters. The result shows that the presence of vortex viscosity parameter retards the fluid velocity and hence the heat transfer rate is decreased. Also, the non-uniformity parameter affects the fluid flow and heat transfer rate especially for higher Rayleigh numbers. (C) 2017 Elsevier Ltd. All rights reserved.