Natural convection heat transfer and fluid flow is investigated, numerically, inside a tilted wavy walled enclosure. Simulating solar air heater, flat ceiling is considered as cover (cold temperature) of solar air heater and wavy wall as absorber hot temperature). The low describing equations are presented in, 1wo dimensional in Cartesian coordinates, dimensionless form by introducing appropriate dimensionless independent and dependent variables. The dimensionless form of the governing equations is solved by using the finite divided difference technique. Solving these equations, the temperature distribution and the hydrodynamic flow field in the enclosure are predicted and accordingly, local and average Nusselt number can be calculated. The effects of system parameters on the natural convection heat transfer inside enclosure are simulated. These parameters are Rayleigh number (5x103 ≤Ra≤ 106), the characteristic height ratio of the charnel (1 ≤ A≤ 5) , characteristic geometric ratio (1 ≤ L ≤ 5) and the inclination angle (10° ≤ ø ≤ 60°) on heat transfer performance are investigated considering air as working fluid. The numerical results show that, the character of clockwise rotating vortex is found to be, strongly, depending on problem parameters. Heat transfer is increased with increasing Rayleigh number and characteristic geometric ratio. To suppress the natural convection heat loss effectively, A should be equal to 2, L larger than I and ø between 20° and 40°.