Application (app)-based interventions using smartphones could provide effective alternatives to traditional treatment programs during and beyond the coronavirus disease 2019 pandemic. The current quasi-experimental study with a non-equivalent comparison group tested the effects of a smartphone app-based metacognitive intervention program with weekly mentoring sessions on the meta-cognitive beliefs, psychotic symptoms, and social functioning of individuals with schizophrenia from community psychosocial rehabilitation centers. The study was conducted with 20 participants with severe psychotic symptoms and low social functioning and 24 participants with relatively light psychotic symptoms and good social functioning as a comparison group. For the experimental group, the app-based intervention was combined with weekly contact mentoring sessions over 10 weeks. The comparison group received only the app-based intervention over 10 weekly sessions. No differences were observed between groups' total scores; however, the experimental group showed a tendency toward improved psychotic symptoms and social functioning over time, unlike the comparison group. These findings provide an empirical basis for managing schizophrenia symptoms with smartphone apps. [Journal of Psychosocial Nursing and Mental Health Services, 61(2), 27-37.].