Polyhexamethylene guanidine (PHMG) is an oligomer containing the guanidine moiety. Since PHMG is known to be a strong anti-bacterial effect and low toxicity, it has been used various products such as ingredient of shampoos and wet tissue including humidifier disinfectant. However, maternal and infantile deaths occurred in Korea due to lung disease of unknown cause in 2011. Before the incident, inhalation toxicological study of the humidifier disinfectant was not performed and it was found that the components of the humidifier disinfectant were inhaled into the respiratory tract leading to lung disease such as pulmonary fibrosis. After the incident, it was found that the components of the humidifier disinfectant were inhaled into the respiratory tract, leading to pulmonary disease such as pulmonary fibrosis. A toxicological study of the humidifier disinfectant when inhaled into the respiratory tract was not performed properly before the event. Although PHMG is presumed to be the cause of the humidifier disinfectants, no studies have been reported on in vivo behavior through the inhalation route of PHMG. Therefore, we performed bio-distribution study and pharmakinetics of PHMG with high sensitivity and quantitative methods. This study has presented a labeling method for the radioisotope indium (111In) of PHMG, and shows the behavior and imaging results of PHMG in vivo.