Airborne fine particles (PM2.5) play a major role in air quality. This study focuses on the chemical composition of PM2.5 and its seasonal variation in 2015, based on an 8-month observation campaign in Calgary. Elemental carbon, organic carbon, and nine kinds of water-soluble ions were analyzed in this study. PM2.5 samples were collected by URG-3000ABC air sampler and were analyzed by DRI Model 2001A Thermal/Optical Carbon Analyzer and ICS-2500 ion chromatography. The concentration of PM2.5 has demonstrated a significant seasonal variation with an elevated concentration in summer (13±6μg/m3) and low concentration in winter (9±3μg/m3), which is opposite to most previous studies. Most of the water-soluble inorganic ion components have shown opposite variations. Organics were the main chemical components accounting for 59% of PM2.5. Secondary organic carbon accounted for more than 65% of the total organic carbon. Therefore, the seasonal variation of PM2.5 followed the pattern of SOC.