Background: The aim of this study was to investigate annual changes in pulmonary function in workers who were exposed to inorganic dust. Methods: The subjects were 2,922 male patients who had been diagnosed with pneumoconiosis more than twice during 6 years from 2005 to 2010. Results: Of the 2,922 cases, forced vital capacity (FVC) decreased by 54 mL in 1 year. In contrast, the annual change of forced expiratory volume in one second ($FEV_1$) decreased by 56 mL. Conclusion: This is the first study that has investigated the annual change in pulmonary function in workers exposed to inorganic dust. The results will help estimate the pulmonary condition of patients who are unable to perform a pulmonary function test due to age or a disorder.