Stoma complications may affect physical and psychological aspects in patients’ life. The implementation of counseling and stoma site marking prior to surgery can reduce the risk of complications and improve the quality the life of the patients. Enterostomal Therapy Nurse (ETN) is a nurse graduated of an educational program called ETNEP (Enterostomal Therapy Nurse Education Program). Self-efficacy of ETNs plays vital role in application of counselling and stoma site marking. This study aimed to evaluate knowledge and self-efficacy of ETNs and to investigate the relationship between the knowledge and self-efficacy about counseling and stoma site marking in ETNs. A cross sectional design was used which involved 81 ETNs in Indonesia. The study was conducted in 2017. The data were collected by using online questionnaire in a 3-part on ETNs's demographic characteristics, knowledge of counseling and stoma site marking (27 questions) and self-efficacy (33 questions). The data collecting process designed by google form then analyzed by using Chi Square test. Findings showed that there was a statistically significant correlation between the knowledge and self- efficacy (p=0,008, OR=3,808). An increase in knowledge corresponded with an improvement in the self- efficacy about counseling and stoma site marking in ETNs. This recommended every hospitals with stoma care may improve ETNs knowledge about counseling and stoma site marking periodically.