In traditional English as a foreign language (EFL) speaking classes, students have insufficient time and opportunities to practice (Zhan et al., 2015). In addition, they lack cultural and communicative contexts (Ko et al., 2021) to improve their speaking skills. Furthermore, a large number of students, especially in Asian countries, have low self-efficacy with regard to their English-speaking competence and try to avoid any activities that require speaking in public (Sun et al., 2017). In this study, we designed social language learning (SLL) activities to bridge the above-mentioned gaps and developed a mobile-assisted SLL system to support students' participation in SLL activities. We explored how our SLL activities affect language learners' speaking performance and self-efficacy and investigated their SLL networks and perceived acceptance of the mobile-assisted SLL system. A total of 58 graduate students were recruited for the study and randomly divided into two groups: a control group in which students completed assigned tasks using the traditional method and an experimental group in which students completed assigned tasks using the mobile SLL system. Our results showed that while the speaking skills of students in the two groups improved after the study, the learning gains of the experimental students in EFL fluency, lexis, pronunciation, and content were significantly better than those of the control students. The experimental students significantly outperformed their counterparts on the dimension of culturality, authenticity, and abundance of created verbal content. The self-efficacy of the experimental students was much better than that of the control students. The results also showed that the interaction degree of the experimental students improved, and they positively perceived applications of the mobile-assisted SLL system to EFL learning. Based on the results, several suggestions and precautions were proposed for educators and researchers in the field to consider.