The purpose of this study was to investigate the development of pre-service physics teachers' pedagogical content knowledge (PCK) on the subject of electricity and magnetism after their completion of physics and mathematics courses. A descriptive longitudinal development research was carried out with 13 pre-service teachers (PTs) who completed their subject matter education by the end of the fall term of 2007-2008 academic years. Six of those PTs were selected for further studies on the development of PCK throughout the following three terms. A PCK test, observations, lesson plans and informal interviews were used as data collection instruments. Results showed declines in subject matter knowledge, improvements in representation varieties, and changes in orientations during field-based experience and increases in knowledge of learner difficulties. Past experience, field-based experience, teacher training, written materials, mentor teachers, school context and the nature of subject matter were found as factors affecting the PCK development.