Background: During they work, mobile population must separate from their spouse in a long time, makes them tending to have extramarital sexual relationship. Objective: To describe the high risk sexual behavior and prevention of STD and HIV among mobile population. Methode: Respondents were 825 in size selected purposively in northern coast of Java and North Sumatra, then interviewed using structure questionnaire, while subsample were questioned in-depthly. They were truck and bus drivers, assistant of truck and bus drivers, fishermen or sailormen. Result: Majority of respondents had middle education level (70%) and were married (75%), while their average monthly income was one million rupiah. Nearly half confessed of having extramarital sexual relationship, although only below 20% used condom recently. This unsafe sex was done with casual partner such as sex worker, girl friends or just friends. Their access to get condom or adequate STD treatment were limited. Easy accessed health facility unit was very few. Information about STD and HIV&AIDS majority was from television. Conclusion: This low knowledge level on STD and HIV&AIDS including its treatment might increase the transmission of these diseases from mobile to general population. Providing health service unit close to shelter or terminal of bus and truck, or sea-port, would improve access to information of STD and HIV&AIDS as well as its treatment, besides disseminating it through popular media such as television.