We present an example of defect structure evaluation based on the angular dependence of ESR signals. In silicon crystals, the resonance magnetic field and the g-value of an ESR signal vary with the orientation of the external magnetic field relative to the crystal axes ([100], [110], [111], etc.). Analysis of this angular dependence provides valuable information about the symmetry and electronic structure of vacancy-related defects. Here, we measured the angular dependence of the g-value by varying the direction of the applied magnetic field using a silicon single crystal oriented along the [111] direction.