It has been attempted to suppress cubic-rhombic phase transition of 12SSZ for eliminating a discontinuity in electrical conductivity by making crystallite size finer without resorting to the conventional method of doping with heterogeneous element. Synthesized powder was prepared by the citrate process, and sintered through the SPS method, where the specimen was sintered at lower temperatures with grain growth suppressed. Synthesized powder presented cubic phase with crystallite size about 340 Angstrom. The SPS method provides dense-sintered specimen of cubic phase at the room temperatures after having been sintered at temperatures lower than 1100 degreesC, with crystallite size around 370 Angstrom, while that of air-sintered at 1500 degreesC is as large as 650 Angstrom. The electrical conductivity of SPS specimen increased in the lower temperature range (400-670 degreesC), while decreased in the higher range (680-800 degreesC), in contrast to air-sintered specimen. When the transition point was lowered close to the room temperature, the discontinuity in conductivity at around 670-680 degreesC was eliminated. (C) 2004 Elsevier B.V. All rights reserved.