Abstract: This invention is directed to a novel method for purifying calomel (Hg.sub.2 Cl.sub.2). More particularly, this invention pertains to a novel process for treating impure calomel (Hg.sub.2 Cl.sub.2) to produce a highly purified calomel product that passes American Chemical Society requirements for calomel assay and mercuric chloride contamination. A process for treating impure calomel to produce purified calomel comprising: (a) incorporating impure calomel into an aqueous slurry; (b) oxidizing the aqueous slurry with an oxidizing agent to form soluble mercuric chloride; (c) filtering the aqueous slurry containing soluble mercuric chloride into liquid and solid components; (d) heating the liquid component to greater than 70.degree. C; (e) treating the liquid component with a reducing agent to precipitate purified calomel; and (f) separating the precipitated purified calomel from the filtrate.