The purpose of this study is to investigate the potential and effects of using mobile device games on learning English as a Foreign Language (EFL) vocabulary in a Saudi female public high school. Although English has been taught in Saudia Arabia since 1958, the learning outcomes have not been satisfactory, hence the imperative to research new teaching methods. After conducting pilot studies of five mobile games with teachers and students, The English Bee, an original game specifically designed for this research project, was. selected. The study comprised two participant cohorts: one taught through The English Bee, the other a control group taught by traditional methods. It employed a mixed methodology of a number of collection techniques for both qualitative and quantitative data, namely, pre-and post-tests, focus group discussions, interviews and reflective essays. The results show that using mobile game helps to improve students' achievements in learning EFL vocabulary, in terms of both the spelling of words and pronunciation recognition, as well as in enhancing their positive attitudes towards learning a foreign language. These results will assist other researchers, developers and educationalists worldwide, in choosing or programming games for learning both English and other foreign languages.