The aim of this longitudinal study was to investigate the changes in preservice science teachers' beliefs about science teaching during a science teacher training programme. The study was designed as a panel study, and the data were collected from the same participants at the end of each academic year during a four-year period. The participants were composed of 76 preservice teachers, and the DASTT-C was used as the data collection tool. As a result of the study, it was determined that the students had conventional teaching beliefs after the first years of the teacher training programme. Moreover, the mental teaching styles of preservice teachers about the science teaching were found to undergo changes throughout their undergraduate education. Participants' beliefs about conventional teaching started to change, especially after they first took a science method course in their third year and their beliefs shifted towards student-centred teaching. Implications for science teacher training programmes were also addressed.