Increasing student exposure to autonomy-supportive teaching approaches has been linked to enhanced student intrinsic motivation to learn. However, such approaches are rare in mainland Chinese science classrooms. An intervention-based study with quasi-experimental design and mixed methods was conducted to explore the impact of a 9-month-long autonomy-supportive teaching intervention on a physics teacher and 147 grade 8 students attending a middle school in China. Data collected through questionnaires, interviews, and observations were analyzed to elicit and track shifts in teacher practices and students' perceptions of learning physics at pre-, post-, and follow-up intervention phases. General linear modeling confirmed significant changes in students' perceptions of their learning environment over time in terms autonomy, satisfaction of autonomy needs, and agentic engagement. Interview and observational data analyses confirmed increased use of autonomy-supportive teaching behaviors and provided further insights into teacher and students' perceptions of the impact on student learning.