Background: The prognostic value of serum alkaline phosphatase (S-ALP) has not been fully validated for nasopharyngeal carcinoma (NPC). Materials and Methods: S-ALP levels were measured in 601 patients newly diagnosed with NPC before radical treatment, and possible associations of these levels with 5-year overall survival (OS) and tumor-free survival (TFS) were explored using univariate and multivariate analyses. Results: Elevated pretreatment S-ALP (>85 U/L) was significantly less frequent among patients classified as T1+2 or stage I+II than among those classified as T3+4 or stage III+IV. Multivariate analysis showed that elevated pretreatment S-ALP (>85 U/L), age, T classification and N stage were independent predictors of poor OS and TFS. Conclusions: Pretreatment S-ALP may be a reliable biomarker to evaluate the long-term prognosis of patients with NPC.