The natural convection flow is commonly encountered in many engineering applications, and extensive studies were conducted to analyze the natural convection flow in the vertical and inclined rectangular cavities. However, most published studies assumed the cavity with infinite width and neglected the impact of cavity width. The present work mainly focuses on the natural convective heat transfer in the inclined rectangular cavities with low width-to-height ratios, through both experimental and computational fluid dynamics (CFD) analyses. A three-dimensional (3-D) model is firstly built up using the CFD code Fluent to simulate the airflow movement and convective heat transfer in the inclined rectangular cavity. The 3-D CFD model is then validated by the experiments performed on both the inclined and vertical rectangular cavities. Good agreements are observed between the theoretically simulated and experimentally measured airflow velocities and temperatures, as well as the temperatures of cavity walls. After validation, the 3-D CFD model is employed to analyze the impacts of width on the airflow velocity and convective heat transfer in the cavities with the width-to-height ratios of 1, 2, 4 and 8 respectively. It is concluded that increasing the width-to-height ratio and cavity inclination contributes to accelerate the natural convection flow and enhance the convective heat transfer in the cavity. In addition, the impact of the cavity width-to-height ratio becomes minimal on the natural convection flow, when it increases beyond 4. (C) 2015 Elsevier Ltd. All rights reserved.