Theoretical and experimental studies were carried out on exciton-polaritons excited in ZnO. Polaritons in which both Γ(1) and Γ(5) excitons couple to electromagnetic waves simultaneously are shown to exist, and their signatures are observed in polarized reflectance spectra measured under k is perpendicular to a and E is parallel to c configurations for an m-plane sample. Theoretical calculations reveal that the mixed-mode polaritons consist of one Γ(1) transverse mode and two Γ(5) longitudinal modes. It is also shown that the signatures are sensitive to the valence band ordering.