TE‐TM mode conversion caused by magnetic linear birefringence (MLB) has been studied in liquid‐phase‐epitaxially grown (BiGdLu)3(FeGa)5O12films. The films were grown on Gd3Ga5O12substrates of which the face normal is tilted from the (111) axis by the angle &thgr;c. The LPE growth on the substrate with &thgr;c≠0 made the magnetization of the film tilt from the film normal, and this enabled the mode converter to work without any applied external field. The theory developed to describe the function of the mode converter agreed well with the experimental results. The MLB coefficient is about −9 rad/cm at a wavelength &lgr;=1.15 &mgr;m. The Bi substitution is effective to enhance the MLB effect. A role of the MLB mode converter to realize a simple and compact waveguide optical isolator is discussed.