Inhalation study is a gold standard study to estimate the harmful effect of respirable chemicals. Pulmonary inflammation, fibrosis and tumor are often used as endpoint for pulmonary toxicity of respirable chemicals. The main methods of aerosol generation are direct synthesis method, dry-based method and wet-based method, and the selection of generation method is necessary according to the chemicals. Experimental design should be included to avoid the concentration which is over the overload and prepare the observation period of which persistent inflammation, fibrosis and tumor in the lung could be estimated. The measurement of half times of respirable chemicals in the lung is important to judge to reach to the level of the overload. It is also useful to estimate the pulmonary toxicity of respirable chemicals especially for nanomaterials if the physico-chemical properties of nanomaterials are measured.