Residential coal combustion (RCC) is a major source of atmospheric mercury (Hg) in rural areas of China, but little is known about the isotope signatures of Hg from this source. In the present study, the isotope compositions of speciated Hg (Hg-0, Hg2+, and Hg-p) in flue gas emitted from RCC were investigated in two important coalproducing areas (Xingren (XR) and Jinsha (JS)) of Guizhou Province, Southwest China. The total Hg concentration in discharged flue gas is in the range of 1.80-9.65 mu g/m(3) at the two sites, and the emission ratio reaches 99.87%. Isotope signatures of total Hg in flue gas are similar to those of Hg in feed coal, with near-zero Delta Hg-199 and negative delta Hg-202 (1.47 parts per thousand for XR and 3.00 parts per thousand for JS) in discharged flue gas. Such isotope signatures are very different from those of Hg emissions from modern coal-fired power plants with much higher delta Hg-202 signals. Negative shifts from Hg-0 to Hg2+ in flue gas for delta Hg-202 (-0.94 parts per thousand) and Delta Hg-199 (-0.51 parts per thousand) were observed, suggesting that both mass-dependent fractionation and mass-independent fractionation occurred during RCC. The nuclear volume effect produced by chlorine oxidation of Hg-0 to Hg2+ may play an important role in the observed mass-independent fractionation in Hg2+. Without any air pollution control devices, RCC potentially increases the atmospheric Hg levels and has a negative-shifting impact on the delta Hg-202 of atmospheric Hg.