The purposes of this study were to describe pre-service science teachers’(PTs) perceptions and practices about using history of science(HOS) in their instructions and their experiences as in-service teachers(ITs) and to determine the relationship between PTs perceptions and practices about using HOS in their classrooms. The HOS Instructional Survey was administered to 68 PTs in two different universities in Turkey. After these students had graduated, some questions were asked about their views about practicing integrating the HOS in their instruction to the 19 ITs who started to work in schools. Findings revealed that PTs had favorable level of perceptions and practices about using HOS in their classrooms. Furthermore, PTs’ perceptions are highly correlated with their practices about using HOS in their classrooms. Interview results revealed that after PTs become ITs, in their teaching practices of history of science they emphasized mostly conceptual understanding and the least emphasis given to contextual understanding.