A majority of research on mobile-assisted language learning focuses on traditional English language learners: thus, little attention has been paid to older adult learners. The purpose of the study is to explore the learning experiences of Chinese older adults using the free and popular English learning mobile apps, Duolingo/Hello English, Baicizhan, and Liulishuo, in a self-directed learning (SDL) context. A 17-week sequential mixed-methods study was designed. 55 older adults from age 45 to 85 participated. The informed grounded theory was used and Saldana's coding techniquesfor qualitative analysis. Quantitative data were analyzed using descriptive statistics and paired sample t-tests. Findings demonstrate that older adults persisted in learning using mobile apps for 17 weeks and increased their vocabulary significantly. Finally, a transformational learning model called MISAPP was created based on the empirical data and the SDL theory.