Purpose: Accurately measuring the content knowledge of teachers is critical to designing professional development to support their teaching. We examined the depth of specialized content knowledge (SCK), defined in terms of instructional tasks reported by teachers and factors that could affect their SCK. Method: Content maps were used to evaluate the SCK of 384 Chinese secondary physical education teachers. Teacher demographic variables such as age, gender, educational background, teaching, coaching, and playing histories, and engagement with professional development were also collected. SCK scores were analyzed descriptively. An ANOVA was conducted to investigate demographic variables that could influence SCK scores. Results: Descriptive data showed a majority of teachers (78.2%) had low SCK scores. The ANOVA analysis showed that teachers' ranking position, and years of teaching experience, significantly predicted the SCK score. The remainder of the variables failed to significantly predict the SCK score. A post hoc analysis showed that 1st grade rank teachers scored marginally better than those with a 3rd grade rank. Teachers' years of teaching experience negatively predicted their scores on the content map. Teachers who had more years of teaching experience scored lower on their SCK. Conclusion: A majority of teachers in this study had low SCK. These two statistically significant relationships found were weak but not meaningful. Our findings suggest that SCK, as a special kind of content knowledge, may not be easily obtained from experience.