The general theory of Wannier‐Mott polaron excitonic states is developed using the Pekar‐Fröhlich Hamiltonian of electron‐phonon interaction in a periodic structure consisting of alternating pairs of two different polar semiconductor layers, such as compositional superlattices (SL). The effects of dynamical screening of electron‐phonon interaction by inertial polarization are examined in two limiting cases, namely in the Haken limit with R_ex > R_i and in the Meyer limit with R_ex < R_i,; R_ex, R_i, are the exciton and polaron radii of electron (i = e) or hole (i = h). For the first time the renormalization of the optical vibration spectrum is taken into account, and the exact potential of electron‐hole interaction is used to calculate the size dependent exciton binding energy. The theory is employed to calculate the binding energy of exciton states in GaAs/Al_xGa_1−xAs superlattices.