A new structural polymorph of Li3BP2O8 has been successfully synthesized via a solid-state reaction between Li3PO4 and BPO4 at 4 GPa and 600 degrees C. The high-pressure phase of Li3BP2O8 (HP-Li3BP2O8) was found to crystallize in monoclinic symmetry with the cell parameters of a = 8.57010(4) angstrom, b = 11.11812(5) angstrom, c = 5.55380(3) angstrom, and beta = 97.7269(3)degrees [space group P2(1)/a (No. 14)]. HP-Li3BP2O8 has a new crystal structure that has not been reported so far. The total ionic conductivities measured for the polycrystalline sample by alternating-currrent impedance were 3.4 X 10(-7) and 2.1 X 10(-6) S/cm at 399 and 456 K, respectively. The lithium ionic conductivity of HP-Li3BP2O8 was higher than that of the low-pressure phase Li3BP2O8 in the temperature range of 375-456 K. This is caused by the difference in the dimensions of the lithium arrangements between LP- and HP-Li3BP2O8.