NbTl3Se4 crystallizes in the cubic I-43m space group. The structure is three-dimensional and consists of two NbTl3Se4 frameworks. Nb5+ is bonded in a tetrahedral geometry to four equivalent Se2- atoms. All Nb–Se bond lengths are 2.42 Å. Tl1+ is bonded in a 8-coordinate geometry to four equivalent Se2- atoms. All Tl–Se bond lengths are 3.30 Å. Se2- is bonded in a 1-coordinate geometry to one Nb5+ and three equivalent Tl1+ atoms.