The type of sexual partner especially prostitutes is one important risk factor for HIV and other sexually transmitted disease. Often, the first sexual contact happens without proper protection. This research intended to study the types of first sexual partners and factors influencing the types of first sexual partners using some of the data from the project titled “Determinants of sexual Behavior that Influence the risk of Pregnancy and Diseases among Rural Thai Young adults” conducted in 1995. In addition, a sample group consisting of 288 sexually experienced unmarried male youth were given questionnaires to obtain information about the type of sexual partner. It was found that nearly half of the respondents had first sexual intercourse with prostitutes. About one – third had first sexual intercourse with girlfriends/lovers. The number of those who had first sex with friends and the number of those who had first sex with loose girls were not much different. The results of Multinomial Logistic Regression found that the youth who were in school were more likely to have had sexual intercourse with girlfriends/lovers than loose girls compared to those who were not students. The youth from warm families were more likely to have had sex with friends than to have had first sex with loose girls compared to those from poor families. The youth who lived far from town were more likely to have had first sexual intercourse with girlfriends/lovers than prostitutes compared to those who lived near the town. This research suggests policy measures to promote and upgrade the compulsory education, campaigning for good relationship in families. Moreover, visiting entertainment places of youth should be closely monitored.