Mobile assisted language learning (MALL) has caught the attention of educators and researchers in the recent years. However, there isn’t sufficient empirical studies to prove its effectiveness in promoting English language. This case study which was carried out with 10 Japanese university students, aimed to investigate if HelloTalk, a language exchange learning application, can promote self-regulated learning among the participants. Participants are encouraged to freely use all the features of the mobile application, which include text messages, voice messages, voice-to-text, text-to-voice, translation, free calls, favorites language information (database of foreign language words, sentences, audio files, grammar corrections, or pictures), and grammar corrections, moments and comments, to assist their English learning outside of the classroom. Data is collected from participants’ public posts in the application and interviews. The results suggested that HelloTalk provided a platform for participants to use English more frequently. The opportunity to interact with native speakers in English and the immediate assistance they received from other application users during their learning of English motivated participants and promoted self-regulated learning. However, result also suggested that language teachers should be aware of the social networking features of the application which might be misused for non-language learning purposes.