Dynamical diffraction of light is studied in two-dimensional(2D) optical superlattices. Graphical representations of the directional dispersion of the Floquet-Bloch waves in the structure are given in reciprocal space. We show that the form of the dispersion surface depends critically on the frequency detuning from the Bragg frequency and the ratio of the index modulation strengths in the 2D medium. Analytical expressions for the dispersion surface and the width of the stop gap of the structure are also obtained.