Using renewable energy resources in buildings has been increasing for saving energy. Among widely used methods, solar chimneys absorb solar radiation and induce an airflow for ventilation, heating, or cooling buildings. The performance of a solar chimney depends on the heat transfer in its air channel, which can be modified by changing the shape of the heat exchange surface. In this study, we examine the effects of a rectangular obstacle placed on the heated surface of the air channel of a solar chimney. A numerical model was built with the Computational Fluid Dynamics (CFD) technique. By changing the geometries of the chimney and of the obstacle, and location of the obstacle, it was found that the obstacle had strong effects on the local flow and heat transfer properties close to the object, particularly the Nusselt number and the temperature field. However, average quantities of the whole air channel flow, such as the averaged Nusselt number and the induced flow rate, were modified insignificantly, except for the temperature rise through the chimney and the thermal efficiency. The change of the flow rate and the average Nusselt number was 5.0% while the temperature rises and the thermal efficiency was up to 13.0%. The height of the obstacle had more influence than the length. This study suggests more investigations to achieve the objective of enhancing the induced flow rate for ventilation of buildings with an obstacle in the air channel of a solar chimney.