The effects of teachers' audio feedback on students' project-based learning and its influencing factors have seldom been empirically explored in the higher education context. To address this research gap, a group of Hong Kong freshmen (18-23 years old) and their teachers were involved in this study. Data were collected from students' retrospective journals, post-journal interviews and teacher interviews after the participants experienced audio feedback during their group projects in a General Education course. The findings demonstrated that teachers' audio feedback enhanced students' learning engagement, critical thinking and project output. The students also reported that audio feedback provided convenience, timeliness, rich information, asynchronous discussion and social presence. Other factors including the features of audio feedback, communication between student and teacher on the received feedback and their learning motivation were also crucial in determining the effects of audio feedback on student project-based learning.