Research on teacher education has been shifting from the emphasis on changing teachers' behaviors to investigating how teachers' mental thinking influences their teaching behaviors. Teachers' beliefs and planning are two important components among teacher thinking research. The purposes of this study are to uncover preservice secondary science teachers' beliefs about science and pedagogy and to investigate how preservice science teachers' beliefs about science and pedagogy influence their planning and teaching. This study used qualitative methods such as participation observation, field notes and in-depth interviews. Topics discussed in the interviews included the ways informants planned their lessons, the considerations during their planning, the resources they used in planning, and the reflection on their teaching performance. An open-coding system was generated to analyze data and the data were categorized. The study suggests that although so many preservice teachers articulate similar bliefs, their underlying context may be quite different. Therefore, the best way for science educators to introduce learning theories to their students is for them to explain what they mean by providing substantial reasoning for their responses. Self-reflection on one's action could help these preservice teachers to be aware of their own thinking and performance. (KR)