Understanding of nature of science (NOS) serves as one of the desirable characteristics of science teachers. The current study explored 55 Thai and 110 Bangladeshi in-service secondary science teachers' conceptions of NOS regarding scientific knowledge, scientific method, scientists' work, and scientific enterprise, by using the Myths of Science Questionnaire (MOSQ). The results revealed that Thai and Bangladeshi science teachers had nine different and five similar conceptions of NOS. The most common uninformed NOS conceptions held by both groups were science as cumulative knowledge and a relationship between theories and laws. The most different conceptions of NOS where Thai had more informed conceptions than Bangladeshi participants were science as individual enterprise, creativity and imagination in science, and scientific knowledge coming from experiments. Interestingly, of four subcategories, there were three (i.e. scientific knowledge, method, and enterprise) that Thai science teachers had more informed conceptions than Bangladeshi teachers. The explicit inclusion of NOS in the national science curriculum should be considered. In addition, the pattern of NOS conceptions that emerged from this study can be utilized for designing NOS professional development programs for Asian science teachers.