A neutral-framework thorium oxohydroxosulfate hydrate has been isolated from aqueous solution. This microporous structure, which self-assembles without a templating agent, is built from [Th-6(OH)(4)O-4(H2O)(6)](12+) hexamers and thorium(IV) monomers linked through bridging sulfates. Solution conditions were chosen to enable an active competition between sulfate and hydroxide for thorium coordination. Synthetic requirements are discussed for this rare example of a thorium(IV) polynuclear complex containing mixed oxo-, hydroxo-, and sulfato-bridging moieties.