The purpose of this study were to identify the health-related fitness (HRF) knowledge level of experienced physical education teachers who were selected for guiding and advising the teachers in their regions by Ministry of Education in Turkey, and to examine the HRF knowledge internalization processes of teachers' who were a) high in knowledge level and use it in their classes, b) high in knowledge level but not use in their classes, c) have misconceptions in their knowledge, and d) low in knowledge level. "HRF Knowledge Test" and "HRF Knowledge Level and Teaching Competency Self-Evaluation Scale" were applied to 79 teachers with a mean age of 38.3 (SD=5.4) years, and mean teaching experience of 14.6 (SD=5.3) years. Then, teachers were located in one of the four groups stated within the study purpose, according to their HRF knowledge levels. Four focus group interviews were conducted separately with each group, including 5 or 6 randomly selected teachers from each pre-organized group (totally 22 teachers). In conclusion, it was found that teachers' HRF knowledge was low and teachers' HRF knowledge level and their experiences in knowledge internalization processes were quite different among themselves. In future professional development programs, the focus should be in teachers' specific needs by their HRF knowledge levels.