Experimental and numerical results of heat transfer by mixed convection in a ventilated cavity are presented. The results were obtained for a 1.0 m × 1.0 m × 1.0 m cavity. The inlet and outlet dimensions were of 0.08 m × 0.08 m, and the air velocity at the inlet was set to 0.1 and 0.5 m/s. The left wall receives a uniform and constant heat flux whereas the right wall was maintained at a constant temperature. Experimental and numerical results of temperature profiles and heat transfer coefficients are presented and compared. The results showed that the variation of the Rayleigh number increases about 1% the percentage differences between experimental and numerical values, and the maximum percentage differences on heat transfer coefficients are 2.0% for Ra = 2.7 × 108 and 3.0% for Ra = 4.5 × 108.