This study explores how science teachers’ explicit argumentation instruction influence their nature of science (NOS) understanding and its enactment through a professional development program. The study has a multiple-case study approach with conveniently selected four science teachers. These teachers were from the same school district in the southeast of the United States. Qualitative data were collected through views of nature of science (VNOS) questionnaire and semi-structured interviews to assess the changes in teachers’ views of NOS from the beginning to the end of the study. Teachers’ integration of NOS was examined through classroom observation by taking field notes. The data analysis was conducted through descriptive statistics and constant-comparative method: scores were assigned for the participants’ responses on the VNOS questionnaire, and the frequency of the codes were examined to develop categories and themes. The results presented that four science teachers could not demonstrate substantial changes in their views of NOS; their understandings of the aspects of science were mixed by the end of the study. They showed consistently naive and mixed views, but also there were slight positive or negative changes. For the implementation, science teachers’ use of NOS was different: even though two teachers integrated the characteristics of science explicitly, the other two teachers did not present explicit NOS instruction. The study makes a case for professional development of in-service science teachers. Science teachers should be supported to understand and enact NOS through research-based strategies and explicit NOS instruction approach such as conceptual change framework.