BACKGROUND: Approximately 10% of female athletes have a history of stress fractures, which most commonly occur between the ages of 16 and 17 years old. PURPOSE: We investigated whether tartrate-resistant acid phosphatase 5b (TRACP-5b), which is a bone resorption marker, can serve as a valid predictor of stress fractures in female athletes in their teens and 20s. METHODS: Three hundred and sixteen elite female athletes were recruited between 2013 and 2015. Serum TRACP-5b and various hormones were examined in blood samples. The serum TRACP-5b level was compared between athletes with and without stress fractures within 3 months after the initial collection of their blood samples. RESULTS: The 316 athletes were divided into two age groups: 13-19 years old and 20-29 years old. Thirty-six athletes (11.4%) experienced new stress fractures within 3 months after the initial collection of their blood samples. The median serum TRACP-5b level was significantly higher in teenage athletes with new stress fractures than in teenage athletes without new stress fractures. In univariate logistic regression analysis, the Z-score of serum TRACP-5b was a significant predictive factor of stress fractures in teenage athletes only (odds ratio: 1.87; 95% CI: 1.31-2.66; P < 0.0012). CONCLUSION: For teenage female athletes, TRACP-5b is a predictor of the risk of stress fractures, and measuring TRACP-5b levels may be useful to prevent stress fractures.