Arsenic (As) is considered a carcinogenic toxin, and nonferrous metal smelting activities can release significant quantities of As, causing an increase in As levels in the environment. A total of 221 samples of moss belonging to 5 species in 4 families were collected from the Wanshan District, the world third largest mercury mining area, in Guizhou Province, southwestern China, for analysis of total As (tAs) concentrations and As speciation. The results indicated that the tAs concentrations in these mosses ranged from 0.67 to 9.6 mg kg(-1), with an average of 2.4 +/- 1.7 mg kg(-1). The dominant species of As in these mosses were inorganic forms of arsenite (As(III)) and arsenate (As(V)) with a total percentage of 87%, whereas the concentrations of organic forms (mono-methylarsonic acid (MMA) and dimethylarsinic acid (DMA)) were relatively low, with percentages of 11.8% and 6.0%, respectively. A significant correlation (r = 0.766, p < 0.01) was observed between As(V) and tAs. In the spatial distribution pattern of As, high concentrations of As in mosses were centralized around historical Hg retorting sites in the town of Wanshan, the villages of Gouxi and Yanwuping and sites downwind of these locations, suggesting that historical intensive Hg mining activities might be the most possible source of atmospheric As.