The purpose of this study is to develop teachers' orientations toward teaching science scale from an instructional perspective in a Thai context. The scale consisted of nine orientations with 54 items. The pilot data were collected from 125 secondary science teachers in Thailand and analysed by using the Rasch rating scale model with WINSTEPS version 3.57.0. The preliminary analysis showed that all the underlying nine orientations fulfilled the assumption of uni-dimensionality and local independency. However, a total of 11 items were found beyond the acceptable range of person or item fit statistics. Findings revealed the satisfactory level of item reliability for all the nine orientations, but unsatisfactory level of person reliability for four orientations. Results support the need to develop more items that cover a wide range of difficulty in the main study so that Thai secondary school teachers' orientation toward teaching science can be measured along a continuum.