Half-metallic materials are characterized by the coexistence of metallic behaviour for one electron spin and insulating behaviour for the other. Thus, the electronic density of states is completely spin polarized at the Fermi level, and the conductivity is dominated by these metallic single-spin charge carriers. This exotic physical property could have a significant effect on technological applications related to magnetism and spin electronics. Some ferromagnetic systems, such as Heusler compounds(1) and chromium dioxide(2), have been predicted theoretically to be half-metallic. However, a half-metallic system has not been demonstrated directly and the predictions are still in doubt(3,4). Here we report spin-resolved photoemission measurements of a ferromagnetic manganese perovskite, La0.7Sr0.3MnO3, which directly manifest the half-metallic nature well below the Curie temperature. For the majority spin, the photoemission spectrum clearly shows a metallic Fermi cut-off, whereas for the minority spin, it shows an insulating gap with disappearance of spectral weight at similar to 0.6 eV binding energy.