The present article aimed at understanding those unvoiced biases pre-service teachers may have that conflicts with their integration of nature of science in their science lessons. Three senior pre-service science teachers' views on NOS with regard to their decision making on critical incidents and their reflections about how they contextualize science teaching were investigated in science method course. The findings indicated that, pre-service science teachers varied in reflective their nature of science understanding in different contexts related to their science teaching approach. Therefore, current study suggested that efforts to improve science teachers' nature of science views and practice need to consider science teachers' unvoiced biases such as their approach towards science teaching and their decision making related to science teaching.