HIV infection is one of the ten major health problems in the world which is quite worrying and will develop into AIDS if the infection has acquired an advanced stage. In HIV/AIDS patients, the infection can manifest as lesions in the oral cavity. For health workers such as dentists, HIV/AIDS is an infectious disease which requires to beware because treatments in dental care possess a risk of transmitting HIV from sufferers to dentists. Thus, knowledge and good attitude are required as an effort to prevent HIV/AIDS transmission. The objective of this study is to examine the relationship between knowledge and attitude to prevent HIV/AIDS transmission in dental students at Dental student (RSGM), Universitas Muhammadiyah Yogyakarta. This study employed a cross sectional study. The sample of this research is dental students comprising of 65 students. Collecting data administered a questionnaire instrument about knowledge and attitude to prevent HIV/AIDS transmission. Data analysis utilized Spearman Rank Correlation test. The results revealed that 48 respondents (73.8%) owned high knowledge and 33 respondents (50.7%) possessed positive attitude about HIV/AIDS. Spearman Rank Correlation test displayed a significance value of 0.001 (p < 0.05) with a correlation coefficient of 0.404. There is a significant relationship between knowledge and attitude to preventing HIV/AIDS transmission in dental students at Dental Hospital (RSGM) UMY and in general, dental students possess high knowledge and positive attitude.