Chlor-alkali plants (CAPs) are major consumers of mercury (Hg) and may be a source of severe Hg pollution to the environment. In this paper, the total mercury (THg) concentrations and the speciation and mobility of Hg were measured in salt slurry and soils collected from an abandoned CAP in Yunnan Province, China. THg concentrations in the salt slurry samples varied widely and ranged from 0.43 to 2640 mg/kg; THg concentrations varied vertically and were lower towards the surface than deeper in the profile. In the soils, a sample collected from electrolysis workshop had the highest THg concentration (3650 mg/kg). The main fractions of Hg in the salt slurry and soils were Hg²⁺ and Hg⁰, which accounted for 47.4% and 22.9% of THg in the salt slurry and 28.0% and 43.8% of THg in the soils on average, respectively. The Hg⁰ concentrations decreased with depth in the soil profiles. The total soluble Hg (TSHg) concentrations in the salt slurry averaged at 140 μg/L and ranged from 0.77 to 564 μg/L. The salt slurry and soils at the study site were seriously contaminated with Hg, which could potentially be released to the atmosphere or water bodies.