[en] In a normal state (T=300 K) for a monodomen region of a rhombic monocrystal YBa₂Cu₃O_6.55 (T_c=60-70 K) are measured rotation, ellipticity and anisotropy of the Kerr polar magneto-optical effect. The effect in the studied crystals of the 1-2-3 HTSC system is characterized as a linear in the magnetic field strength effect of rotation of the polarization plane of a reflected optical beam. The magneto-optical dissipation parameter is determined for YBa₂Cu₃O_6.5 monocrystals. Measurement results are analyzed within the framework the formal model of magneto-optical response