Recent interest in integrating mobile apps into teaching will continue growing. There remains, however, a pressing need to develop methods and resources to support and educate preservice teachers about the use of these technologies. This case study aimed to examine preservice teachers' criteria for evaluating educational mobile apps. Nineteen fourth-year preservice teachers, who studied math, science, English, and computer education at a public university, participated in the research. During the usability tests, the preservice teachers were asked to evaluate the affordances and limitations of selected educational mobile apps from their particular subject domains. Their interactions with and evaluations of the mobile apps were collected through think-aloud sessions and interviews. Qualitative analysis revealed preservice teachers' evaluation criteria in five categories such as pedagogy, technical usability, content, connectivity, and contextuality. The results point to recommendations for future research on evaluating the capabilities of existing mobile apps with key players such as in-service and preservice teachers.