The chlor-alkali industry, which is one of the largest mercury (Hg) consumption and emission sectors in China, may lead to serious Hg pollution of the environment. In this study, we investigated Hg contamination in groundwater, stream water and sediment, the atmosphere, and soil around an abandoned chlor-alkali plant (CAP) in southwest China. The results indicated that the dissolved mercury (DHg) concentrations in groundwater within the CAP exceeded the national limit in 46.4% of the samples, and that this was a result of Hg leaching from upper contaminated salt slurry and soil. Moreover, THg concentrations of surface water and sediment were highly elevated, with maximum levels of 1940 ng/L and 74.6 mg/kg, respectively. Total gaseous mercury (TGM) levels inside the plant were also significantly elevated compared with those outside, which indicated the impact of Hg release from the salty slurry. The THg enrichment factors in surrounding soils ranged from 1.56 to 22.5 (with a mean of 7.18) compared with the regional background, while 28.6% exceeded the second-grade national limit of China. The spatial distribution of THg concentrations in the surrounding soils revealed a unique pattern, with a peak 1-1.25 km from the CAP. Overall, the results indicate that Hg release from the CAP has caused serious pollution of the surrounding environment.