In order to assess the seasonal variation, potential sources, and health risk of heavy metals found in fine particulate matter (PM2.5), PM2.5 samples (n = 96) were collected between March 2015 and February 2016 in Ningbo, China. Twelve heavy metals (Sb, As, Cd, Cr, Pb, Mn, Ni, Se, Tl, Al, Be and Hg) found in PM2.5 were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). We used enrichment factor and principal component analysis/absolute principal component scores (PCA/APCS) to determine the sources of these heavy metals. We used models from the United States Environmental Protection Agency (EPA) to assess both carcinogenic and non-carcinogenic risk of heavy metals to adults and children. Results showed that the annual average mass concentration for PM2.5 was 62.7 μg m−3, which is higher than the Chinese National Ambient Air Quality Standards (NAAQS). The annual average concentrations of Pb, Cd, and As were 57.2 ng m−3, 1.5 ng m−3, 4.7 ng m−3, respectively, which were below the limits of the NAAQS. The highest concentrations of the total heavy metals occurred in winter, and the lowest concentrations were observed in summer. Enrichment factor analysis indicated that Sb, Cd, Pb, Se, As and Tl were mainly from anthropogenic sources. Source apportionment by PCA/APCS indicated four major sources: coal combustion and motor vehicles (46.3%), soil and construction dust (37.1%), steel works (6.9%) and other smelting industries (6.8%). The carcinogenic risk of heavy metals in Ningbo was lower than the safe level for both children and adults. However, the total non-carcinogenic risk was higher than the safe level (HI=1.38). This warrants further research to explore air pollution sources and implement effective measures to control air pollution in Ningbo, China.