The paper deals with the synthesis and structure of FeCl3-CrO3-graphite bi-intercalation compound (FeCl3-CrO3-GBC) prepared during the subsequent intercalation of chromium trioxide into stage-2 FeCl3-GIC/graphite system. From the results of the X-ray diffraction measurements and the scanning electron microscopy coupled with energy dispersive X-ray analysis it was concluded that the product consists of a mixture of saturated FeCl3-CrO3-GBC and stage-2 FeCl3-GIC. Based on the model of the transformation from stage-2 FeCl3-GIC/graphite system to FeCl3-CrO3-GBC, it can be understood that upon the subsequent intercalation process CrO3is intercalated in the interlayer spacings of graphite both free and occupied by FeCl3. Due to the latter invasion the double-layer co-intercalation domain is formed whereas a part of FeCl3is displaced to the zone of the pristine graphite present in the host FeCl3-GIC.