The present study was conducted to investigate the impact of using a brain-based learning program for optimizing EFL in-service teachers' professional delivery of instruction. The study used the quasi- experimental research design (pre-post control-experimental design). Thirty-six EFL in-service   teachers enrolled in the professional diploma- Methodology Branch- at the Faculty of Education were randomly assigned to two intact groups: experimental(n=18) and control(n=18). The participants in the experimental group only were instructed using a brain-based learning program whereas their counterparts did not receive such training as they received regular instruction. Instruments of the study included a questionnaire of teachers' professional instruction, a checklist of BB lesson design strategies, a test of brain-based learning strategies and a rubric of positivist e-portfolio. The findings revealed that the participants in the experimental group significantly surpassed their counterparts in the control group in the post-performance on the checklist of brain-based lesson design strategies, a test of brain-based learning strategies and a rubric of positivist e-portfolio.