Discipline is an attitude and deed or behavior that can be supported by students in the form of students’ habit in performing and obeying regulations in an orderly manner in accordance with the existing rules. In addition, discipline is defined as a character that needs to be trained for all students, including teenage students who are in high school. The discipline quite often becomes the responsibility of all schools, both guidance and counseling teachers, assisted by subject teachers, class teachers, staffs and school principals. This study aims to determine the constraint and strategy of Guidance and Counseling teacher in increasing students' discipline in Sleman High School. This study is a qualitative research, a type of phenomenology, data collected by observation, interviews and questionnaires. Participants in this study were 15 guidance and counceling teachers, from high school level in Sleman Regency, Yogyakarta, Indonesia. Data analysis used is quantitative descriptive technique. The data was analyzed by Milles & Huberman with data reduction, data presentation, verification of the conclusion. The result of this paper showed that the strategy of Guidance and Counseling teacher had a positive impact in enhancing the students' disciplinary behavior as well as being able to shape the character of students to be better human being.