Exciton‐polariton mode splitting of quantum wells (QWs) in a microcavity is experimentally and theoretically investigated under a high magnetic field up to 14.5 T. The magnetic field dependence of the splitting interval has been measured for the precisely tuned photon and exciton mode. It is found that the splitting interval increases with an increase of the magnetic field, which shows enhancement of magnetoexciton‐photon interaction. Theoretical analysis using a transfer matrix method and a variational method demonstrates that these properties are mainly caused by the increase of exciton oscillator strength due to the magnetic field. The effect of the number of QWs on the mode splitting is also discussed. ©1996 American Institute of Physics.