The diffracted and the transmitted rocking curves for GaAs(200) in the symmetric Laue case are observed near the Ga K-absorption edge by using the synchrotron radiation. The quantitative comparison between the measured transmitted rocking curves and the corresponding calculated ones based on the dynamical theory of X-ray diffraction has been cattied out, and the anomalous scattering factors for Ga K-absorption edge in GaAs have been determined.