Peplau was one of the first nursing theorists who developed the theory of interpersonal relations. She was born in 1909 in Pensilvania, USA and graduated from the nursing school at Portstown hospital, obtained her master`s degree in psychology at Banington University in 1943, followed by master`s degree in mental health nursing from the college of education at Columbia university in 1947, and in PhD in nursing in 1953. The clinical practice of Peplau includes US army, private hospital, general hospital, along with nursing research and education, and she opened her clinic for mental health nursing. She published "Interpersonal Relations in Nursing" in 1952, in which she clearly identified nursing phenomena related to interpersonal relations between nurse and patients from the perspectives of clinical practice, research, and education. The theoretical background of Peplau was influenced by Sullivan, and the Peplau`s theory was based on literature reviews on behavioral science, and theories of Sigmund Freud, Erich Fromm, Abraham Maslow, and Neal Miller. At the beginning of her theoretical building, she integrated her theory into psychoanalysis, social learning theory, human motivation theory, and human development theory. Through her publication, she emphasized that the major concern of nursing theory should on promoting nursing practice, on which her theory on interpersonal relations between nurse and patients was based to develop therapeutic interpersonal relations to promote individual health. Peplau`s theory contributes to establish nursing professionalism which improve nursing practice by expanding body of nursing knowledge. She has served the president of American Nurses Association (1970-1972), consultant of World Health Organization, and numerous publications to develop nursing professionalism until her retirement in 1974. Her theory was utilized to establish the concepts of mental health nursing. Not only for mental health nursing area, however, nursing practice is based on interpersonal relations between nurse and patients, her theory should be able to apply to in most, if not all, areas. This paper is to introduce Peplau`s theory of nursing and its utilization in nursing practice through literature review.