This study is to more clearly identify the problems of students' vocabulary achievement in distance learning and how the use of Android applications as a way of mobile learning to address the problem. This study aims to examine the effectiveness of the mobile learning concept with the use of a learning source named Lima Sahabat for learning vocabulary among seventh-grade students of junior high school. A Pre-experimental research design was used (one group Pre-Test and Post-Test design). The population in this study were all the seventh-grade students (64 students) and the sample was class VII B (31 students) which was chosen by using purposive sampling. The finding of the data analysis showed that the mean score of the Post-Test (88.84) was higher than the Pre-Test (55.83) with the improvement percentage was 59.13% and the success rate of the students' score in the difference of the Pre-Test and the Post-Test showed that the p-value = 0.00 was less than the α = 0.05 which means that there was a significant improvement of the students' vocabulary achievement.