摘要:Special theory of relativity is one of the difficult subjects of physics to be understood by the students. The current research designed as a qualitative research aim to determine the pre-service physics teachers’ understanding level and the alternative conceptions about three core concepts of special theory of relativity, such as time dilatation, length contraction and reference frames. The data were collected through semi structured interviews and were analyzed by using content analysis. At the end of the analysis process the understanding level of the students was determined to be “complete understanding”, “incomplete understanding” and “misunderstanding”. In order to achieve this, the students’ conceptual frameworks based on the operational definitions made by the students were determined firstly. The findings obtained in this research indicate that high school teachers as well as university instructors should take special care with some points in the teaching of the subjects related with special theory of relativity. This research might be useful to other studies to be done in the future, especially for investigating the students’ mental models related to special theory of relativity.