Mercury is frequently found in minerals associated with gold and silver ores. One of the main challenges in gold processing plants using cyanide is that cyanide also leaches elements other than gold and silver. One of these elements is mercury. Mercury forms very stable complexes with cyanide ions which create environmental and technical problems at the leaching, carbon adsorption, elution, and electrowinning stages of gold production. Ammoniacal thiosulfate is one of the most promising alternatives to cyanide for the leaching of gold. This paper reports the dissolution behaviour of different mercury compounds (elementary mercury (Hg0), mercuric chloride (HgCl2), mercurous chloride (Hg2Cl2), and mercury sulfide (HgS) in ammoniacal thiosulfate leaching solutions. Thiosulfate solutions are shown to dissolve mercury similar to cyanide, which would need to be considered when thiosulfate is used to leach gold. Mercuric chloride was the most soluble of the mercury salts tested with the order of the rate of dissolution in thiosulfate solutions being HgS < Hg0 < Hg2Cl2