The purpose of this study is to investigate how the in-service science teachers' (IST) perceptions and practices about curriculum and integration of the history of science (HOS) and the nature of science (NOS) affect their science courses. For this aim, how ISTs integrated the NOS and HOS in their elementary science courses for understanding of the NOS, the results of this integration, and how the ISTs' NOS views influenced their science teaching practices were examined. In this phenomenological study purpose and criterion sampling methods were used. Nine ISTs constituted the sample of the study. A constant comparative method was utilized for the data analysis. Multiple data sources and different evaluators were used for triangulation. The current study revealed that all the teachers in the study do their best to implement the science and technological curriculum; however, the implementation of the curriculum is not at the expected level. Also our findings indicated that the teachers' views about NOS did not directly influence their educational practices. In addition, knowing how to teach NOS is an important factor for a teacher's transfer of their knowledge and understanding of NOS to their classroom, as well as the teacher's NOS views. In this process some possible problems such as creating misconceptions, not explaining the NOS aspects effectively, differences in the students' beliefs, individual differences, and problems in the classroom environment might emerge and negatively affect the teachers' integration of NOS and HOS.