The purpose of this study was to develop an assessment instrument to assess secondary school mathematics teachers’ assessment practices. The instrument employed a two-layer rubric scale. Based on the literature review, this instrument was developed with two main components: (1) mathematics teacher’s characteristics; and (2) mathematics teacher’s assessment practices. For the first component, the mathematics teachers’ characteristics encompassed four constructs including teachers’ belief and values, teachers' knowledge, teachers’ skills and teachers’ attitudes. The second component, which is teachers' practices, comprised of five constructs including learning outcomes, subjects blueprint, expected target result, folio A and folio B. It is hoped that this article will provide an overview of the instrument to assess secondary school mathematics teachers’ assessment practice.