The purpose of this study is to characterize heavy metals in ambient PM10 (particles with aerodynamic diameter below 10 µm) and PM2.5 (particles with aerodynamic diameter below 2.5 µm) particles in a typical integrated iron and steel industry zone (HG) and a background site (ZWY) during February 2011 to January 2012 in the Yangtze River Delta (YRD) region, China. Twelve elements were measured to study their levels, size distribution and sources. At the two sampling sites, Fe was found as the dominated metal in the total detected metals in both particle sizes, followed by Zn and Pb. They were regarded as the marker elements of iron and steel production emission along with Cr and Mn. The concentrations of all measured heavy metals in HG were 1–3.53 times higher than those measured in ZWY. When compared with previous studies, the concentrations of steel related elements (Fe, Zn, Mn) in this work were significantly high. The highest correlation coefficient was observed in HG for Fe and Zn. Additionally, Cd was found as the most enriched heavy metal by the enrichment factor analysis, followed by Zn, Pb, and Cu. The main sources contributing to heavy metals at HG site were identified by principle component analysis: steel dust (including coal combustion of coal-fired power plant, coke making and steel making emission), vehicle emission and road re-suspension dust and soil dust. Besides, steel dust was also found as the possible source of heavy metals at ZWY site. The result suggested the steel dust has influence on the whole study area.