Abstract A new member of the A 2 B 5 C 5 X 16 family of compounds – the first one containing Se – has been synthesized. Following a one-step mechanochemical synthesis route, starting from the binary selenides and Mg metal, Cu 2 Mg 5 Sn 5 Se 16 has been obtained. Structural evaluation was carried out using X-ray diffraction with subsequent Rietveld refinement. Cu 2 Mg 5 Sn 5 Se 16 adopts the spinel type with space group Fd 3‾ $\overline{3}$ m and exhibits a statistical distribution of Cu, Mg, and Sn on Wyckoff position 16 d whereas Wyckoff position 8 a is only occupied by Mg. Despite the fact that structures containing MgSe 4 tetrahedra are rare in the literature, it appeared to be the most plausible way of distributing the cations in this compound.