The concentrations of PM2.5, carbonaceous aerosols, O3, NOx, SO2 were measured from a haze event in Wuxi City, Jiangsu, China from Dec. 21th to Dec. 26th, 2013. Aerosol extinction coefficient and depolarization ratio were measured by micro-pulse polarization lidar. Characteristics of air pollutants in haze days were analysed. The haze event last for 3.4 days and fine particles were the main pollutants. Hourly average mass concentration of PM2.5 was 131.04 μg·m-3, and 183.75 μg·m-3 in haze days which was 2.98 times higher than in normal days. Total carbon (TC), which was strongly correlated (correlation coefficients=0.790) with PM2.5, accounted for 24.18% of the mass concentration of PM2.5. In haze days, the ratio of TC to PM2.5 was 16.65%, lower than that in normal days (34.38%). This suggested that secondary inorganic particles might have a fast increase in haze days, which led to a high concentration of PM2.5. The concentration of O3, affected greatly by solar radiation, showed less variation both in haze days and normal days. The volume fraction of NOx and SO2 in haze days was 1.66 which was 1.68 times higher than in normal days, respectively. The increase concentration of SO2 was not only related to local accumulation but also can be affected by sulfur-rich particles from external transmission; the sulfur-rich particles might inhibit the heterogeneous reaction of SO2.