Circularly-polarized and angular-resolved magneto-photoluminescence spectroscopy was carried out to study the free A exciton 1S state in wurtzite ZnO at 5 K. The Γ symmetry of the top valence band symmetry is confirmed according to the unique selection rules of Zeeman splitting lines. The out-of-plane component B of the magnetic field, which is parallel to ZnO's c-axis, leads to linear Zeeman splitting of both the dipole-allowed Γ exciton state and the weakly allowed Γ/Γ exciton states. The in-plane field B, which is perpendicular to the c-axis, increases the oscillator strength of the weak Γ/Γ states by forming a mixed exciton state. For the Γ symmetry, the lower energy Zeeman splitting peak of the weak Γ /Γ can only be σ polarization. © IOP Publishing and Deutsche Physikalische Gesellschaft.