The research objective of this study was to compare the relative effectiveness of history of science (HOS) integrated instruction and curriculum-oriented instruction on sixth grade students' understanding of nature of science (NOS). Accordingly, two classes were assigned to experimental group and other two were assigned to comparison group randomly. Experimental group was instructed by contextualized explicit and reflective approach in lessons that utilized history of science instruction on circulatory system while comparison group followed regular curricular activities suggested in national science curriculum. Both groups' NOS views were compared with pre, post and follow up measurements using VNOS-E. The result showed that, experimental group students' NOS views regarding targeted aspects improved in varying degrees after HOS instruction. The improvement in students' NOS views was discussed by attributing to contextualized, explicit and reflective NOS instruction.