The disparity between theoretical knowledge and practical application in undergraduate education poses a formidable challenge, potentially burdening students’ cognitive load. In response, e-portfolios have emerged as a promising solution, capable of fostering self-directed learning and promoting students’ ownership of the quality of their educational outcomes. This study investigates the impact of employing e-portfolios for reflective practices on learning efficiency and cognitive load among Thai undergraduate students. The sample comprised twenty English major undergraduates selected through purposive sampling from a university in Thailand. Employing a mixed-methods experimental design, the intervention involved incorporating reflection activities (i.e., writing a learning log) through e-portfolios. Pre- and post-tests, coupled with a cognitive load survey, were administered, while qualitative data were collected to delve into participants’ attitudes and perspectives. The results revealed a significant improvement in post-test scores when compared to pre-test scores (Cohen’s d = 0.891), underscoring the substantial impact of the intervention. Additionally, the average cognitive load exhibited a decrease in intrinsic and extraneous load, while the automatic load remained unchanged. In addition, student interviewees believed that reflections through e-portfolios could help them learn better, but also expressed some issues with its utlization. However, a small sample could influence the generalizability. These findings hold practical implications for leveraging reflection through e-portfolios to enhance learning efficacy, promote a comprehensive understanding of lessons, and foster self-monitoring of academic progress.