Small hollow nanocubes of the ternary spinel ZnxCo1-xCo2O4 of ca. 18 nm dimension were prepared via a facile hydrothermal route. A growth mechanism is suggested in which solid single-crystal Co3O4 nanocubes are gradually converted to hollow single-crystal ZnxCo1-xCo2O4 nanocubes with preservation of the spinel framework through differential diffusion of Zn2+ and Co2+ ions. With the cation exchange, the chemical composition and thus physical properties can be tailored.