It is shown from experiment that a rotaion &rgr; and a deformation &khgr; of the optical indicatrix appear during the transverse field‐induced phase transition in hematite. Strong dependence of &rgr; and &khgr; on the temperature, magnetic fieldHaand the angle &PSgr; corresponding to the direction ofHawith respect to theC2axis in the basal plane are observed. During the Morin transition, the evolution of the linear magnetic birefringence is very sensitive to the magnetic phase transition and this evolution is discussed from the dependences of the analytical expressions of &rgr; and &khgr; on the rotation of the antiferromagnetic vector L.