The quantization axis, which is one of the principal axes of the zero-field splitting tensor, can be determined by means of the EPR two-circle goniometer. The sets of two dimensional angles of the orientations on the principal plane perpendicular to the quantization axis have been calculated according to the orthogonality of vectors. One can measure the EPR spectrum of different orientations based on the calculated sets of two dimensional angles, and specify the two other principal axes. In this way, one can determine the Eulerian angles by which the laboratory axis system (x, y, z) are related to the principal axis system (X, Y. Z). The procedure has been applied to the measurement of X band EPR data for Cr3+-doped Na3(AlMo6O24H6)·8H2O single crystal as an illustrative example.