This study presents an initial version of an e-learning system that assists learners of Japanese with their study of vocabulary. The system uses sentences from a corpus to generate context-based exercises. The sentences used in the context-based exercises are selected using a readability formula developed for this system. We used the system with two different types of corpora, a web corpus that we constructed for this system and a sample of the recently released Balanced Corpus of Contemporary Written Japanese (BCCWJ). We compared the two corpora and while the BCCWJ has better word coverage, our web corpus still covered a majority (96.1%) of the target vocabulary words even though it's relatively small. Evaluation of this system showed that the readability formula performs well, especially when sentences contain the system's target set of vocabulary words. A group of learners of Japanese were also asked to use the system and then fill out a survey. Results of the survey indicate that the learners thought the system was easy to use. Most of the learners also expressed a desire to use this type of system when studying vocabulary.