This study surveyed a private girls’ high school in Taipei about students’ flipped learning readiness in their English-as-a-foreign-language (EFL) classrooms, and explored the effects of their personal characteristics on the readiness levels. The personal characteristics included academic levels, test performance, the availability of outside-school support and resources, and their preference on group activities. The results indicated the flipped learning readiness consists of five factors; they are technology self-efficacy, motivation of English learning, self-directedness and learner control, in-class communication, and willingness of doing preview. The five readiness factors differ significantly. Regarding the effects of personal characteristics, academic levels made no impact, but the availability of outside school support and resources had significant effects on some readiness factors. It is hoped that the findings shed light on high school students’ flipped learning readiness for their EFL learning and provide some insights for EFL teachers to design more adaptive instruction in flipped classrooms.