This study aims at investigating the impact of brain-based learning on the retention of English language knowledge amongst young adult learners. The participants were subjected to an intervention in brain-based learning principles for approximately four and a half months. The results of the proficiency exams administered at the beginning of and following the intervention were analysed in an effort to explore whether brain-based learning intervention exerts impact on the improvement of participants' proficiency in English. With a view to examining knowledge retention, the results of the retention exam administered six months after the post-proficiency exam were analysed. An interview was conducted both after the post-proficiency and the retention exam to gain insights into the participants' views of the brain-based learning intervention. The findings attained from the analysis of both quantitative and qualitative data yield that establishing a learning environment compatible with brain-based learning principles enables knowledge retention.