Abstract: Objective To explore the concentration of particulate matter less than 2.5 microm in aerodynamic diameter(PM2.5) and its health effect among residents in Harbin city.Methods The data on atmospheric PM2.5 concentration,meteorologic factors,the numbers out-patients with respiratory diseases,and mortality of respiratory diseases in Daoli and Daowai district of Harbin city from 2009 to 2011 were collected and analyzed.The risk of respiratory diseases associated with PM2.5 was evaluated.Results The results showed that the concentration of PM2.5 increased year by year and was significantly higher in heating period(from November of the year to April of the next year) compared to that of other months(P<0.05).The concentration of PM2.5 was inversely correlated with the daily average temperature and monthly rainfall(r=-0.623,P=0.006 and r=-0.606,P=0.008)(P<0.001).The number of outpatients visiting the Department of Respiratory Disease of the Second Municipal Hospital of Harbin city increased significantly in heating period,with the increased proportions of 11.6%,18.9%,and 35.8% for the year of 2009 to 2011 and the PM2.5 concentration in the heating period of the three year was 44,95,and 60 μg/m³,respectively.Conclusion The concentration of PM2.5 in Harbin city was 1.97-2.66 times higher than the national standard and PM2.5 pollution was especially serious and associated with the number of outpatients visiting respinatory disease departmen during heating period in Harbin city.