The crystal structure has been determined for one of the monoclinic modifications of Sn2P2Se. There are P2S6-groups in the structure with nearly undistorted point group summetry 3̄m. These are connected to a threedimensional network by 7-fold and 8-fold coordinated tin-atoms. The crystallographic data of the cell are: α0 = 9.378(5) Å, b0 =7.488(5) Å, c0 = 6.513(5) Å, β = 91,15°(5), Ζ = 2. The space group is nearly P21/n but slightly distorted to Pn.