Background: In 2017, incidence of STI accounted for 54.6% of all communicable diseases. Syphilis, gonorrhea and trichomoniasis per 10000 populations are higher than the national average and congenital syphilis has been registered regularly over the past 5 years, which is a major problem today. Thus the study aims to research the knowledge, attitude and practice of sexually transmitted diseases in adults of Dornod Aimag. Methods: The population of Dornod aimag was divided into 4 clusters and one cluster from the aimag center and remaining 3 clusters from soums were selected for the study based on the ratio of population aged between 16-49 years. Random sampling was used to select participants from aimag center and 13 soums and total of 342 people selected for the study. Results: Knowledge of sexually transmitted diseases is insufficient. There is no difference in the level of knowledge of sexually transmitted infections between men and women (p = 0.352). There is a difference in the level of knowledge between age groups and the knowledge level increases with age (p = 0.001). For the question about casual sexual behavior, 21.1% of respondents had casual sex intercourse 2-5 times. Gender differences were seen in attitudes toward casual sex, as 27.8% of male and 14.5% of females had casual sex 2-5 times (p=0.000). 18.1% of respondents used condoms during casual sex, while 13.5% occasionally used condoms, and considering the gender of participants, 24.9% of men and 11.6% of women (p = 0.000) used condom during casual sex. Conclusion In Dornod aimag, there is a lack of awareness of STI and risk behaviors. Furthermore, they have no intention to protect their health due to lack of positive attitude and commitment to protect their sexual health.