The increasing popularity of mobile-assisted vocabulary learning (MAVL) has called for empirical research studies to explore its effectiveness in promoting learning from a stakeholders perspective. In this regard, the present study aimed to investigate Korean adult learners’ use of a mobile application for learning new English vocabulary, with a focus on learning process, learning outcome, and learners’ perception of the vocabulary learning using a mobile application. Forty university students took part in an experiment using a pre-post test design which involved completing vocabulary tests, using an application to self-study assigned words, keeping a study log, and filling out questionnaires. Results showed that learning gain was statistically significant with the use of the application, with participants utilizing a wide variety of approaches to learning vocabulary. Learners reported that the use of the mobile application helped to increase their concentration, confidence, and sense of achievement. In general, learners found the MAVL useful, satisfactory, and beneficial for vocabulary learning, and many of them stated their intention to use mobile applications for future vocabulary learning. Individual differences among learners are further discussed in the study, as well as confounding factors affecting learners’ perception of the vocabulary learning using a mobile application and pedagogical implications.