The aim of this study is to introduce an activity on magnetic fields prepared in order to improve high school students' views on the nature of science. The activity was prepared according to explicit-reflective approach, which is one of the nature of science teaching methods. The nature of science elements intended to obtain with the activity are as follows: Changeability of scientific knowledge, its empirical nature, its subjective nature, its partly being a product of creativity and imagination, the difference between observation and inference. The activity on magnetic field lines was prepared including these elements and was expert reviewed. After revisions were made according to the views of experts, a pilot activity was implemented with five 12th grade students. The video recordings, observation notes, activity papers used in the process and opinions of the students in the activity were analyzed. At the end of the study, it was found that the students were not able to make the distinction between observation and inference; however, the desired level was reached with respect to other elements using explicit-reflective approach.