We examine the superconducting anisotropy γc = (mc/m ab ) 1/2 of a metallic high-Tc superconductor MgB2 by measuring the magnetic torque of a single crystal. The anisotropy γc does not depend sensitively on the applied magnetic field at 10 K. We obtain the anisotropy parameter γc = 4.31 ± 0.14. The torque curve shows the sharp hysteresis peak when the field is applied parallel to the boron layers. This comes from the intrinsic pinning and is experimental evidence for the occurrence of superconductivity in the boron layers. \pacs{74.25. Ha,

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