Objective: Limited data are available concerning sexual behavior of Korean men.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 HW/AIDS,Methods: 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.