A high-nuclearity mixed transition metal/actinide complex has been prepared from the reaction of a Mn-4(III) complex with Th(NO3)(4) in MeCN/MeOH. The complex [Th6Mn10O22(OH)(2)(O2CPh)(16)(NO3)(2)-(H2O)(8)] is the largest such complex to date and the first Th/Mn species. It is rich in oxide groups, which stabilize all of the metals in the high Th-IV and Mn-IV oxidation levels. Magnetic characterization establishes that the complex has an S = 3 ground-state spin value.