The objective of this study is to facilitate progressive transitions in chemistry teachers understanding of nature of science in the context of historical controversies. Selected controversies referred to episodes that form part of the chemistry curriculum both at secondary and university freshman level. The study is based on 17 in-service teachers who had registered for an 11-week course on "Investigation in the teaching of chemistry" as part of their Master's degree program. The course is based on 17 readings drawing on a history and philosophy of science perspective with special reference to controversial episodes in the chemistry curriculum. Course activities included written reports, class room discussions based on participants' presentations, and written exams. Based on the results obtained it is suggested that this study facilitated the following progressive transitions in teachers' understanding of nature of science: (a) Problematic nature of the scientific method, objectivity and the empirical basis of science; (b) Myths associated with respect to the nature of science and teaching chemistry; (c) Science does not develop by appealing to objectivity in an absolute sense, as creativity and presuppositions also play a crucial role; (d) The role of speculation and controversy in the construction of knowledge based on episodes from the chemistry curriculum; (e) How did Bohr confirm his postulates? This goes beyond the treatment in most textbooks; (f) Differentiation between the idealized scientific law and the observations. It is concluded that given the opportunity to reflect, discuss and participate in a series of course activities based on various controversial episodes, teachers' understanding of nature of science can be enhanced.