This paper presents and discusses the results of an experimental programme carried out to study the behaviour of steel tubular members under axial compression in empty, normal mortar-filled, and aerated mortar-filled conditions. Nine specimens with outer diameter-to-wall thickness ratio 25.33 and length-to-outer diameter ratio 3 were tested and the load-deformation curves and failure patterns obtained are presented. Results indicate that presence of mortar in the tubes not only enhances the load carrying and energy absorbing capacities but also delays the formation of first peak load.