This study investigated the effectiveness of flash card games in enhancing vocabulary retention among university students at a university in northern Viet Nam and examined students’ responses to this vocabulary learning technique. The study employed a classroom action research design involving planning, action, observation, and reflection. Data were collected through a vocabulary pre-test, a post-test, and a closed-ended questionnaire. The pre-test was administered before the intervention to identify students’ initial vocabulary achievement, while the post-test measured vocabulary retention after students learned vocabulary through flash card games. Questionnaire data were used to explore students’ perceptions of the technique. The findings showed that students’ vocabulary achievement improved after the intervention. Students’ responses were also largely positive, indicating that flash card games made vocabulary learning more interesting, enjoyable, understandable, motivating, and active. The study concludes that flash card games can be an effective and practical technique for improving vocabulary retention in university EFL classrooms, especially where traditional memorization remains a common classroom practice. The findings suggest that English teachers should integrate visual and game-based activities into vocabulary instruction to promote learner engagement and long-term word recall.