The effect of concave curvature on the natural convection has been numerically studied using the higher-order finite difference method. The heating wall in a enclosure is approximated by a cosine function. The heat transfer coefficient is analyzed for three Rayleigh numbers and five amplitudes. For Ra = 10⁸ the separation and reattachment are observed on the adiabatic walls. The wall heat transfer are slightly changed by the increasing curvatures.