Study Of Types Activity Radioisotope Content In Reservoir Sample At Ulumbu Desa Wewo Kecamatan Satarmese Center Manggarai Regency. Study of types activity mass radioisotope content in reservoir sample at desa Wewo district Satarmese center of Manggarai regency has been done. The aims of this study are to determine radioisotop mass types activity interval, contamination level and the spreading location radioisotope by surveying, sampling, laboratory analyse and intepretation. The results showed that radioisotope mass type activity interval in sample water are 2,216x10-3μCi/gram to 1,095 x 10-7μCi/gram. To the contaminated area at PLTU Ulumbu location and Ulumbu crater, level of radioisotope contamination at the survey location is include to the high alpha contamination (sample 1 and sample 2) at PLTU Ulumbu. At the sampling points (15, 19, 21,23) at Ulumbu crater the intermediate alpha contamination and low betha contamination. Whereas sampling points of 3, 4, 6, 7, 8 and 10 are the area of high contamination for alpha radiation, spreading equally at PLTU Ulumbu. The sampling points of 5 and 9 are the intermediate contamination area for alpha radiation and low intermination for betha radiation. Whereas the sampling points of 11 to 25 at the Ulumbu crater have the low alpha and betha contamination, which its spreading equally. Keywords: Radioisotop, mass type activity, contamination.