While substantial empirical research has been conducted on the efficacy of mobile-assisted language learning (MALL) in enhancing English proficiency, there remains a paucity of studies examining its specific effects on Afghan English as a Foreign Language (EFL) learners. This study addresses this gap by investigating the influence of mobile applications on vocabulary development among EFL students in Afghanistan. A mixed-methods research design was employed, integrating quantitative and qualitative data to ensure comprehensive analysis. The study sample comprised 20 intermediate-level EFL learners from a language institute in Herat, Afghanistan. The research procedure followed a structured sequence: Pre-test – baseline assessment of participants’ vocabulary knowledge, intervention; three weeks of structured mobile application usage for vocabulary training; post-test – evaluation of vocabulary retention and acquisition. Subsequently, semi-structured interviews conducted with five purposively selected participants to collect in-depth qualitative insights. The quantitative analysis revealed a statistically significant improvement (p < 0.05) in participants’ vocabulary retention post-intervention, suggesting a strong positive correlation between mobile application usage and lexical knowledge enhancement. Qualitative data further supported these findings, with interviewees reporting increased engagement and retention due to interactive and spaced-repetition features of the apps. The study concluded with pedagogical implications for teachers and policy makers.