Mercury(I) bromide or mercurous bromide is the chemical compound composed of mercury and bromine with the formula Hg2Br2.

It changes color from white to yellow when heated[1] and fluoresces a salmon color when exposed to ultraviolet light.

[4] A very rare mineral form is called kuzminite and has the chemical formula Hg2(Br,Cl)2.

[4] In common with other Hg(I) (mercurous) compounds which contain linear X-Hg-Hg-X units, Hg2Br2 contains linear BrHg2Br units with an Hg-Hg bond length of 249 pm (Hg-Hg in the metal is 300 pm) and an Hg-Br bond length of 271 pm.

[5] The overall coordination of each Hg atom is octahedral as, in addition to the two nearest neighbours, there are four other Br atoms at 332 pm.