A method of producing β-SiAlON includes a sintering process, in which β-SiAlON starting materials, a mixture of silicon nitride, aluminum nitride, optically active element compound, and at least one compound selected from aluminum oxide and silicon oxide, are sintered at temperatures ranging from 1820° C. to 2200° C. The method provides new β-SiAlON low in carbon content and having high luminescence intensity by placing a plurality of boron nitride vessels in a graphite box to allow the β-SiAlON starting materials packed in the plurality of boron nitride vessels to easily come in contact with nitrogen gas, and performing sintering in nitrogen atmosphere.