Objective: This study aimed to perform the national sex survey and to collect the basic data for establishment of the prevention strategies of sexually transmitted infections (STIs) and HIV/AIDS. Design and Method: This is a national survey performed on a sample of 2,500 individuals (1,273 men and 1,227 women) aged 18-69 years old. The online surveys were carried out on a national scale in South Korea. Subjects were randomly selected from resident registration. A structured questionnaire was developed which elicited information concerning: demographic information, information on their sexual behavior, sexual identity, prostitution, experience of STIs, and experience of sex education. Results: The majority of the subjects were either married or living with a partner. Mean number of sexual intercourse is 3.0±3.3 times a month. Mean sexual satisfaction score using visual analog scale is 63.2±24.6. Eighty-four percent had a fixed sex partner; 13.1% (22.6% of men; 2.5% of women) had experience through a speed dating or prostitution. 0.9% of men and 1.1% of women were sexually attracted to the same gender only, 1.5% of men and 2.0% of women were sexually attracted to both gender. 1.8% of participants had the experience of the STIs. Only 10.4% of the respondents had received sex education in the past year. Conclusions: We performed the National Sex Survey according to the nationwide distribution of population. It would be useful for establishment of the prevention strategies of STIs and HIV/AIDS. To control STIs and HIV/AIDS, powerful policies containing sex education and medical services will be needed.