Single crystals of apatite-type praseodymium silicate (Pr-9.33(SiO4)(6)O-2) and samarium silicate (Sm-9.33(SiO4)(6)O-2) with high oxide ionic conductivity have been grown by the floating zone method. The as-grown crystals of Pr-9.33(SiO4)(6)O-2 and Sm-9.33(SiO4)(6)O-2 are green and orange, respectively, and both crystals are transparent. The crystals do not contain inclusions, low-angle grain boundaries or twin structures but the samarium silicate crystals contain a few cracks perpendicular to the c-axis whereas the praseodymium silicate crystals are crack-free. Microcracks are also introduced in the samarium silicate crystals during the cutting and polishing processes. The oxide ionic conductivities of these crystals are comparable to that of neodymium silicate with the same structure.