By using an appropriate coordinate transform we have calculated variationally the ground state exciton binding energy in the single square well under the tilted magnetic field. The dependence of the binding energy to the magnetic field strength, well width, and the direction of the field is discussed. We conclude that for small well widths the exciton binding energy is very sensitive to the tilt angle. (C) 2000 American Institute of Physics. [S0021-8979(00)05517-1].