Marriage Law has determined the minimum age for marriage is 19 years old men and 16 years old women. However, in the practice there are many occurrence of underage marriage such as in Sleman. This study aims to determine the government's efforts, especially the on Sleman Dinas Pemberdayaan Perempuan dan Perlindungan Anak, Pengendalian Penduduk dan Keluarga Berencana (DP3AP2KB) in preventing under-age marriage and the factors in supporting the government. The research type is normative empirical research. The data in this study used primary data and secondary data. This research used descriptive data analysis techniques with a qualitative approach. The results of this study are the government's efforts, especially DP3AP2KB to prevent underage marriage by creating programs such as the Information Center for Counseling Youth/Students (ICRS/M) that was developed in the program Youth Generation (GenRe) which is managed from, by and for Youth/Students in order to provide information and counseling on marriage age maturation. In the other hand to support the underage marriage DP3AP2KB is making district programs Eligible Children (KLA) and Kampung KB Sleman and conduct socialization to the youth and society. However, the programs were is not effective enough for prevent underage marriage. It was only reduce the number of underage marriage