Background: The low knowledge of HIV / AIDS prevention among adolescents affects adolescent attitudes toward premarital sexual behavior so as to increase the vulnerability of adolescents to acquire HIV / AIDS Research Purpose: This study aims to determine the knowledge of prevention of HIV / AIDS in students at the University of Muhammadiyah Yogyakarta Research Method: The research design is quantitative descriptive with cross sectional approach. Sampling technique using simple random sampling as much as 536 students. Research ni using questionnaires made by the researchers and have tested the validity of biserial correlation coefficient on 30 respondents with r table number 0.361 and reliability using KR-20 with the result 0.916. This research was conducted at Muhammadiyah University of Yogyakarta The results: Respondents of most of the late adolescents with age 19 years counted 345 (64,4%). Most of the respondents were female 296 (55.2%). Respondents in UMY students mostly have HIV / AIDS prevention in good category as many as 489 respondents (90,7%) Conclusions: prevention knowledge of HIV/AIDS among students at Muhammadiyah University of Yogyakarta is good.