Although researchers have achieved some success in effective nature of science (NOS) teaching, helping teachers teach NOS continues to be a great challenge. The development of an educative teachers' guide would provide support for NOS teaching. In this study, we explored the effects that a research-based guide had on affording elementary school teachers' NOS teaching and on improving their students' understanding of NOS, and investigated key features for designing a NOS teachers' guide. The design of the teachers' guide was based mainly on (1) criteria pertaining to educative curriculum materials, (2) previous research concerning teachers' guides as facilitators of science teachers, and (3) feedback from participants of NOS professional-development workshops. Our study sampled 10 teachers who implemented the NOS-curriculum material. Six of them (Group A) had NOS-learning experience, while the other four teachers (Group B) did not. Data sources included student outcomes on NOS, teachers' teaching performance of NOS instruction, an open-ended questionnaire, and transcripts of a focus-group interview. The results indicate that the teachers' guide enables teachers to perceive changes in their beliefs, knowledge, and intention with regard to integrating NOS into the curriculum. Group B exhibited NOS-teaching performance similar to that exhibited by Group A. Group B teachers are capable of improving students' understanding of NOS through the use of the guide. Three key features for designing NOS teachers' guides are: (1) explicitly indicating NOS teaching practice, (2) building pedagogical knowledge for NOS teaching, and (3) guiding teachers' reflection and learning. (Contains 7 tables and 2 figures.)