  The process of photon splitting, becomes allowed in the presence of strong
magnetic field. We calculate the influence of magnetized plasma on the photon
splitting absorption coefficient. We calculate the refraction coefficients and
polarization vectors with the inclusion of the vacuum terms at an arbitrary
value of the magnetic field, and then find photon splitting matrix element
taking into account the terms that vanish in vacuum, but may be nonzero in the
presence of plasma. We find the photon splitting rate in plasma with the
density typical for a neutron star star atmosphere and identify a region of the
parameter space where the plasma effects are important.
