Na3SbSe3 was obtained by solid state reaction of anhydrous Na2Se, antimony, and selenium in a ratio of 3:2:3. It is air and moisture sensitive and melts at 870 K. Yellow single crystals of Na3SbSe3 were used for single-crystal X-ray diffraction. It crystallizes in the cubic space group P213 (No. 198) with a = 9.0227(2) angstrom, V = 734.53(3) angstrom 3, and Z = 4. Na3SbS3 is isotypic with Na3AsS3. Trigonal SbSe3 pyramids therein act as mono-, bi-, and tridentate ligands to sodium. Sodium is located at three different sites, which are all coordinated by six selenium atoms, providing a strongly distorted octahedral environment. NaSe6 octahedra of identical type share common vertices; in case of different sites also face sharing is observed. Na3SbSe3 shows temperature dependent Na+ conductivity above 380 K, which increases to 2.9? x?106 O1 cm1 at 590 K.