Employment of idioms is essential to reach higher English expressive levels, especially for English as Foreign Language (EFL) learners. However, English idioms are challenging for both instructors and learners because the complex content of idioms depends on understanding their cultural context. Most mobile language applications are for vocabulary acquisition. Therefore, the purpose of this study was to develop an animation/video-based application, "My English Idiom Learning Assistant" (MEILA), to explore the different idiom learning behaviors, as well as the relationships of their learning behaviors to MEILA. To explore the relationship between the learning outcomes and the learning behaviors, the researcher used logs from the MEILA database. The participants consisted of 59 freshmen from two English conversation classes in one private university in central Taiwan. Students experienced the learning activities over 3 weeks. The researcher adopted idiomatic understanding pre- and posttests for the study as well as in-depth interviews. The results revealed that MEILA significantly enhanced idiomatic learning outcomes. The sequential analysis used provides language instructors an example of monitoring learning behaviors to improve teaching materials and methods. The findings may stimulate more mobile-assist language learning (MALL) researchers, English instructors, and app designers to create innovative mobile environments for English idiomatic learning.