Although extracurricular music activities are common in Hong Kong, private music teachers' perceptions of children with autism spectrum disorder (ASD) are underexplored in research in this context. This study examined private music teachers' knowledge of ASD and their attitudes toward students with ASD in Hong Kong, and the relationship between these two factors. The study collected data from a questionnaire survey (n = 200) and eleven individual interviews. Unexpectedly, the findings showed that the teachers had a good understanding and a marginally positive perception of ASD, despite some anxiety about teaching students with ASD. Furthermore, knowledge of and attitude toward ASD were positively correlated. Teachers with previous training in special education needs had a better understanding of ASD and a more positive attitude toward ASD than those without related training. These results imply that further formal and public education could promote acceptance of and equal learning opportunities for students with ASD.