Transition metal chalcogenides with yolk-shell nanostructures are a family of promising electrocatalytic materials with complex interior construction and remarkable structural tenability. In this work, a sequence of yolk shell transition metal sulfide nanospheres (Co-Ni-MoSx, Co-MoSx and Ni-MoSx) are prepared as superior Pt-free catalysts for dye-sensitized solar cells. This yolk-shell structure, consisting of a thin shell and an inner porous core, exposes more active sites and provides more contact regions between the electrolyte and catalyst. By comparing with the ternary Co-MoSx and Ni-MoSx nanospheres, the quaternary Co-Ni-MoSx nanospheres have advantages of the relatively larger surface area, favourable chemical composition, higher conductivity and excellent catalytic performance for expediting the reduction of I-3(-) in solar cells. Particularly, as for Co-Ni-MoSx, a splendid power conversion efficiency of 9.76% is achieved under a standard irradiation, which is much better than that of Pt (8.24%).