Young children and elders, who spend most of their time at home, are at high risk of indoor air pollution. Therefore, it is important to take appropriate measures to reduce the levels of air pollutants, in particular, PM. This study determined the elemental characteristics of indoor PM2.5 concentrations in ger, house, and apartments where fuel types were different. The indoor air samples of PM2.5 and elemental chemical species in each ger were collected and measured from December 2019 to August 2020 in 18 ger houses and apartments in the residential area (Songino-Khairkhan district) and city center area (Bayanzurkh district) of Ulaanbaatar. In this study, we used inductively coupled plasma mass spectrometry (ICP-OES) to evaluate the PM2.5 bound elemental composition. Average indoor PM2.5 concentrations were 94.24 and 42.07 µg/m 3 in residential and city centers for the winter, and 12.06 and 23.51 µg/m 3 for the summer period, respectively. In the PM2.5 samples, high concentrations of ambient elements were observed for Ca, Al, K, Zn, and Pb. The concentration of toxic heavy metals such as Pb was 1.4 times higher than the Mongolian National Standard (MNS 4585:2016, which is 1 µg/m 3 ). In conclusion, the seasonal variation of the elements' concentrations mostly depended on consumption, such as coal and wood consumption (W/S > 1). Crustal matter elements depended on dusting and vacuuming activities (W/S < 1). In addition to elements, there are other air pollutants in indoor that should be identified and quantified to estimate the health effects due to indoor air pollution, such as elemental carbon (EC) and organic compounds. Thus, it is warranted to further study the levels of air pollutants in indoor, especially in the residential area in Ulaanbaatar.