A new metal chalcogenide, γ-Hg₃S₂Br₂ (1), has been prepared by moderate-temperature solid- state reaction, and its crystal structure was determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in space group Cmmm of orthorhombic system with a = 9.1923(18), b = 18.2262(5), c = 4.6251(7) Å, V = 774.9(3) ų and Z = 4. In the structure, two Hg(1), two Hg(2) and four S(1) atoms form a near square Hg₄S₄, and such squares are linked by Hg(3) atoms nearly linearly coordinated to two S1 atoms of two parallel Hg₄S₄ squares to form one-dimensional infinite Hg₆S₄ chains along c direction. Optical absorption spectra reveal the presence of sharp optical gap of 2.80 eV for 1. IR spectrum, TGA and electric resistivity have been investigated.