Large GdCa4O(BO3)(3) crystal has been grown by the Czochralski method. The quality of GdCa4O(BO3)(3) crystal was assessed by white-beam synchrotron radiation topography. It has been found that there is a sub-grain boundary in the GdCa4O(BO3)(3) crystal. The boundary divides the large GdCa4O(BO3)(3) crystal into two individuals. Due to the misorientation between the two individuals, the image shifts can be observed in the synchrotron topographs. Based on the misorientation determined by high resolution X-ray diffractometer, the image shifts were calculated for several reflections. The calculations are in agreement with the measurements from the topographs very well. In addition, the formation mechanism of sub-grain boundary is discussed.