The purposes of this study were to investigate science teachers' nature of science (NOS) views so as to determine how their views influence their instructional practices. Seventy four science teachers and five teachers in a big city in Turkey were selected purposefully as the sample of this study. A sub-set of 18 relevant items from Views on Science-Technology-Society (VOSTS) Questionnaire were used to assess teachers' NOS views. Semi-structured interviews and class observations were conducted with these five "case" teachers in order to allow them fully express their views and instructional practices. The data analysis revealed that the participating science teachers held naive views on many dimensions of the NOS. Furthermore, it was found that teachers' views did not directly influence their classroom practices. We also observed that the perceived curriculum, the high stakes examinations, expectations of school administrators, students, and parents were the most important factors influencing teachers' decisions regarding classroom practices.