  The impact of axion-like particles on the light polarization around the
horizon of suppermassive black hole (SMBH) is discussed in the light of the
latest polarization measurement of the Event Horizon Telescope (EHT). We
investigate different sources of the polarization due to axion interaction with
photons and the magnetic field of SMBH. These can modify the linear and
circular polarization parameters of the emitted light. We have shown that a
significant circular polarization can be produced via the photon scattering
from the background magnetic field with axions as off-shell particles. This can
further constrain the parameter space of ultralight axion-like particles and
their couplings with photons. The future precise measurements of circular
polarization can probe the features of ultralight axions in the near vicinity
of SMBH.
