The compounds K0.91U1.79S6 and KU2Se6, members of the AAn2Q6 actinide family (A = alkali metal or Tl; An = Th or U; Q = S, Se, or Te), have been synthesized from US2, K2S, and S at 1273 K and U, K2Se, and Se at 1173 K, respectively. KU2Se6 shows Curie-Weiss behavior above 30 K and no magnetic ordering down to 5 K. The value of mu(eff) is 2.95(1) mu(B)/U. Its electronic spectrum shows the peaks characteristic of 5f-5f transitions. It is a semiconductor with an activation energy of 0.27 eV for electrical conduction. Both K0.91U1.79S6 and KU2Se6 crystallize in space group Immm of the orthorhombic system and are of the KTh2Se6 structure type. Both contain infinite one-dimensional linear Q-Q chains characteristic of the AAn2Q6 family. Typical of the known AAn2Q6 compounds, in KU2Se6, there are two alternating Se-Se distances of 2.703(2) and 2.855(2) A, both much longer than an Se-Se single bond. In contrast, in K0.91U1.79S6, the first sulfide of this family to be characterized structurally, there are alternating normal S2(2-) pairs 2.097(5) A in length. In K0.91U1.79S6, the formal oxidation state of U is 4+.