The sources and characteristics of particulate matter (PM) were determined in a modern underground chrome mine in Finland. Measurements were conducted at five locations in the mine: the maintenance area, blasting area, ore pit dumping area, crushing station and conveyor belt. The measurement set-up consisted of a Soot Particle Aerosol Mass Spectrometer (SP-AMS) for the particles’ chemical composition; an Electrical Low Pressure Impactor, Nano Scanning Mobility Particle Sizer and Optical Particle Counter for the particle number and mass size distribution; and an Aethalometer for black carbon (BC). The particle number and mass concentration depended strongly on the measurement location and period. The PM10 and the total number concentrations varied from 22 to 1100 µg m–3 and 1.7 × 103 to 2.3 × 105 # cm–3, respectively, in the mine. In terms of the composition, the sub-micrometer particles (PM1) consisted mostly of organic matter and BC, but at the blasting site, the fraction of sulfate was also significant. The SP-AMS data was analyzed with Positive Matrix Factorization (PMF) to identify and quantify the main sources of PM1 in the mine. Based on the PMF analysis, the PM1 originated mostly from diesel engines (35–84%) and blasting (7–60%). The impact of blasting on air quality in mines may become more pronounced in the future as the emissions from diesel engines decrease due to alternative fuels and better engine and after-treatment technologies.