[Th(Cp'')3] (Cp'' = {C5H3(SiMe3)2-1,3}) activates P4 to give [{Th(Cp'')3}2(μ-η(1):η(1)-P4)] (1), which has an unprecedented cyclo-P4 binding mode. DFT studies were performed on a model of 1 to probe the bonding in this system.