Introduction: According to World Health Organization, air pollution is a major environmental risk to health and is estimated to cause approximately 1.6 million premature deaths worldwide per year. The air pollution of Ulaanbaatar city is rising year after year.Goal: The aim of this study was to define the lung function of adults in Ulaanbaatar.Materials and Methods: 1196 adults were randomly chosen aged over 20 years of Ulaanbaatar city. Of them 238 subjects were excluded because they had at least one of the following: a history of lung diseases including asthma, COPD, pulmonary tuberculosis, lung fibrosis; symptoms of chronic cough, wheeze, or dyspnea; history of thoracic surgery; history of major acute illness in the past 3 months; or a history of respiratory tract infection in the past 4 weeks. Besides demographic data, information on smoking habits was collected. The lung ventilation function of subjects was checked using a spirometry EasyOne, calculating the indexes Forced expiratory volume 1sec (FEV1), forced vital capacity (FVC), FEV1/FVC ratio. Lung function measurements followed a standardized protocol and fulfilled the ATS criteria.Results: Of the respondents, 486 were males (50.7%) and 472 were females (49.3%). There was a negative correlation between each lung function and age (p<0.05). The lung function was significantly lower in female than in male, for FEV1, FVC (male - FEV1 3.66±0.659 L, FVC 4.467±0.716 L, female-FEV1 2.663+0.559 L, FVC 3.237+0.586 L). In overall, FVC, FEV1 was decreased by 34.5, 37.2 percent, respectively compared with European LLN value.Conclusion: The mean value for FEV1, FVC, FEV1/FVC ratio was 3.17±0.78 L, 3.86+0.89 L and 82.02±6.75 % in overall, respectively.