The title mol-ecule, C(13)H(4)O(2)S(5), is folded by 47.83 (6)° along the S⋯S vector of the [1,4]dithiine six-membered ring, with the naphtho-quinone and [1,3]dithiole-2-thione moieties being nearly planar [largest deviations from least-squares planes = 0.028 (2) and 0.016 (1) Å, respectively]. This boat conformation is close to that observed in the analogous compound [Mendez-Rojas et al. (2001). J. Chem. Crystallogr.31, 17-28] including a 2-oxo group [folding angle: 42.3 (1)° at 213 (2) K]. Both compounds are indeed isomorphous, and the small difference in the folding angle probably results from the involvement of the thioxo group of the title compound in inter-molecular S⋯S contacts [3.5761 (13) Å]. In the crystal structure, mol-ecules are stacked in the [100] direction, with dithiole rings making π-π inter-actions. In a stack, alternating short and long separations are observed between the centroids of dithiole rings, 3.5254 (17) and 4.7010 (18) Å.