An experimental study has been carried out to investigate a synergistic effect of Ba4CuPt2O9 compounds on the critical current density to fluorine-doped YBCO superconductors. The Ba4CuPt2O9 compounds were synthesized by a solid state reaction. It was found that the synthesis temperature of the Ba4CuPt2O9 compounds was over 800 degrees C, which was higher than that of a paper ever reported. In addition, the influence of the Ba4CuPt2O9 compounds on the critical current density to the YBCO superconductors has been investigated to use two types of Ba4CuPt2O9 compound. One is not heat-treated, i.e., source materials, and the other is heat-treated at 950 degrees C. It was found that the former affected the orientation of c-axes, but the latter did not have an influence on the orientation to the c-axes, and molested the superconductivity to the samples quenched at temperatures above 850 degrees C.