The present study is concerned with the pulmonary pathological changes in the rats following intra-tracheal administration of sintering dust and vanadium slag separately. The results indicated that both the volume of lungs and the quantity of pulmonary collagen protein in the treated groups were higher than those in the control groups. The histopathological observations revealed foci of dust cells and fibers in the pulmonary alveoli, bronchi and around the blood vessels, a small amount of reticular fibers and collagenous fibers were also seen. At the same time bronchitis, pulmonary emphysema and atelectasis can also be seen. The pathological changes in the vanadium slag groups were more distinct than those in the sintering dust groups. The paper briefly discussed these pathological changes from the standpoint of the chemical composition of the dusts, dose-response relation, etc.