This paper reports on how and why proficient learners of English in Hong Kong participated in popular culture, out-of-class activities, with an emphasis on their development of learner autonomy. Autonomy in language learning is defined as an individual's ability and responsibility to take charge of his or her own learning [1]. Out-of-class learning plays an important role in language learning and learner autonomy [2]. However, to most Hong Kong students, opportunities to learn English outside of classroom may not be obviously found but they do exist at a low cost, for example, popular culture like English movies, free English TV channels, online resources, social networking [2-4]. Most local learners seldom engaged in actual autonomous practices but they must seize the chances to practise the target language [5, 6]. Thus, the study aimed at exploring how students can make better use of popular culture, out-of-class learning and foster greater learner autonomy in the local context. Six highly proficient secondary school students who reported to have participated in out-of-class learning were selected to join this largely qualitative multiple-case study. By way of semi-structured interviews and language learning journals, the study found that the case participants mainly engaged in self-initiated, interest-driven out-of-class learning, through which they improved their school performance and started to internalize English learning for their personal purposes and develop learner autonomy. It is also suggested that out-of-class learning and school performance promoted the growth of each other. Teachers should recognize the use of interest-driven, popular culture out-of-class activities to further establish the link between out-of-class and classroom-based learning.