The amount of industrial wastes with asbestos such as dismantled construction materials has increased. We have reviewed the effect of asbestos-containing products subjected to harmless treatment on the lungs. Usually, the harmless treatment of asbestos is confirmed by the disappearance of fibrous materials and crystal structures by electron microscopy and X-ray diffraction. However, it is very important to perform animal studies and in vitro studies in order to examine the effect of the treated asbestos-containing products on the lungs. From previous treatments of asbestos using acids or high temperature, almost treated materials tended to show decreased toxicity in vitro and in vivo studies. There are some reports of the adverse effects of the treatment. If new harmless treatments of asbestos are developed, it is necessary to perform animal studies and in vitro studies of asbestos-containing products using new harmless treatments.