Abstract This paper analyzes laminar natural convection of micropolar fluid in a trapezoidal cavity with a local heater. The bottom and top walls of the enclosure are adiabatic while the left vertical wall and part of the right inclined wall are kept at low and high constant tempratures, respectively. The rest part of the inclined wall is adiabatic. Governing equations formulated in dimensionless variables such as stream function, linear vorticity, angular vorticity and temperature have been solved by finite difference method of the second order accuracy. Computations have been carried out to analyze the effects of Rayleigh number, Prandtl number, vortex viscosity parameter and the heater location on streamlines, isotherms and vorticity profiles as well as the variation of the average Nusselt number and fluid flow rate. It has been shown that bottom position of the heater reflects the heat transfer enhancement.