The present research aimed at enhancing EFL in-service teachers' assessment literacy. This was achieved through applying a Blended Backward  Design Model based Program. The research adopted one group design with pre/post test treatment. The sample consisted of 25 EFL in-service teachers. The following instruments were designed and used: An assessment literacy questionnaire;  A Pre/Post Test assessment knowledge test; An observation checklist to observe EFL in-service teachers' assessment performance inside the class. Results of the research indicated that there were statistically significant differences at 0.05 level between the mean scores of the research group on the pre/post administrations of the pre/post assessment knowledge test, and the observation checklist in favour of the post administration. The research group teachers post performance was better than their pre- performance in the target skills.  Consequently, the proposed Blended Backward Design Model Based Program proved to be effective in developing EFL in-service teachers' assessment literacy. Keywords: Blended Learning, Backward Design Model, Assessment Literacy.