Ba 5 (PO 4 ) 3 X (X: OH − , Cl − , Br − ) have been synthesized by the solid-state reaction methods. The X-ray excited luminescent properties of these compounds were investigated, and chloride and bromide compounds showed broad emission band with the peak center at about 400nm while no luminescence of Ba 5 (PO 4 ) 3 OH had been observed. The structure of Ba 5 (PO 4 ) 3 OH was redetermined by X-ray powder diffraction methods and the result of Rietveld refinement is P6 3 /m, a=10.1327(3)Å and c=7.7526(3)Å. The ionic conductivity measurement of Ba 5 (PO 4 ) 3 OH showed its ionic conductivity reached the maximum of 2.0×10 −6 S/cm at 400°C with an activation energy as low as 0.43eV due to the activity of OH groups along the channels.