The research aimed to study the lifestyle of Thai undergraduate students living with HIV/AIDS, particularly their behavioral patterns before contracting the HIV agent, after being diagnosed and at the present stage of their condition. We use a phenomenological technique to gather data from 19 volunteer students who were attending private and governmental universities and who had been diagnosed as having HIV/AIDS. Data were collected by in-depth interviews, on which a content analysis was performed. The results demonstrated that students’ lifestyle could be categorized into three periods of study: Before contracting the HIV agent, they were not raised by their parents but by close family relatives. They had their first sexual experience as early as at 13 years of age; hence, condoms were not used with their sex partner because of intimacy and trust. Moreover, they had at least two and more than 100 sex partners. They acceded to voluntary counseling for HIV blood testing, because of the opportunity disease’s manifestation. After being diagnosed, most mentally had no suicidal ideas, due to they received moral support from their family, lover and close friends, who had witnessed and accepted with their condition. Access to treatment, 17 cases took antiretroviral (ARV) drugs with starting drugs taking the lowest age at nine year old, but two cases did not take ARV, only practicing, self-health care. At the present time, they improved lifestyle, general health behavior, and sexual behavior, feeling of healthier and had positive relationships, especially with close family members and friends. Their future expectations were to achieving a graduate diploma with further on self-development, family and social responsibility. They intended to succeed in their studies and to have employment to secure their own future, and voluntarily assisting social development.