Forest fires are annual problem during the dry season and become a biggest threat to forest resources in Indonesia. The forest fires release into the atmosphere large quantities of particulate matter and volatilized substances. The present study investigates effects of forest fire on air quality in the case of a radiological event of ashes from forest fires emissions in Riau province during an intense forest fire season that occurred in 2015. Atmospheric aerosol samples were collected from May to December, 2015 using a large volume TSP (total suspended particles) sampler. Concentrations of radionuclides in airborne particulate matter were measured by using gamma spectrometry. It was shown that the activity concentrations of 226 Ra, 232 Th and 40 K ranged from 0.026 to 0.114 mBq/m 3 , 0.005 to 0.011 mBq/m 3 and 0.99 to 5.64 mBq/m 3 , respectively. The activity concentrations of 137 Cs in air was found lower than the minimum detectable activity of the gamma counting systems (