Emissions of fine particulates of grade PM2.5 and PM10 from different oil shale (OS) power plant (PP) boilers were studied. Pulverized (PF) and circulating fluidized-bed (CFB) boilers burning oil shale, biomass and retort gas were investigated. Particle emissions from OS boilers were found to be very fine. Over 90% of emitted particulate matter was in the size range of PM10 and 40-60% under the size of 2.5 µm. Distribution of fine particles by size was found to be depending on OS firing mode (PF or CFB). At CFB firing mode the share of the finest fraction PM2.5 was higher than that at PF firing mode. The distribution varied at the same type of different PF boilers, depending on the efficiency of boiler flue gas cleaning system and value of total suspended particulates' emission (TSP).