In the present study, extraction of rare earth elements (La, Ce, and Tb) in phosphor using concentrated sulfuric acid followed by water extraction was investigated in order to develop a recycling process of waste phosphor containing rare earth elements (La, Ce, and Tb). As a pretreatment, Y and Eu were leached with 2.0 mol/dm3 sulfuric acid solution. More than 80% of La, Ce, and Tb were extracted with H2O after heating at 120°C in concentrated sulfuric acid. Extraction efficiencies of La, Ce, and Tb increased with the heating temperature, heating time, and amount of sulfuric acid. A solution containing 5.45 g/dm3 La, 2.57 g/dm3 Ce, and 1.43 g/dm3 Tb was obtained under the condition of 3.00 g sample, 4.00 g sulfuric acid, 120°C heating temperature, 4hrs heating time, and 100 cm3 H2O for extraction.