Science education programs in many countries aim to promote effective teaching and learning process in science classroom and consequently develop scientifically literate person. Science teacher is an important actor to achieve this goal. For this reason, the purpose of the study was to examine the impact of one-week in-service program on elementary science teachers' views of nature of science (NOS). A total of 44 (24 Female, 20 Male) elementary science teachers participated in the study. Pre and post administration of Views On Science-Technology -Society (VOSTS) questionnaire including 14 items (Aikenhead, Ryan & Fleming, 1989) was used to determine teachers' NOS views. The results of the study indicated that at the end of the program majority of teachers' demonstrated substantial improvements in their understanding of some NOS aspects such as theory driven nature of observations, scientific method, and hypothesis. This result supports effectiveness of in-service program on the development of science teachers' NOS views.