Given the limited information regarding the impact of BMI on treatment outcomes for nasopharyngeal carcinoma, we sought to examine the relationship between body mass index (BMI) and cancer control after radiotherapy. We compared clinic outcome information across BMI groups from 1,489 patients treated with radiotherapy between 1990 and 2003. Multivariate analysis was used to determine if BMI significantly predicted adverse recurrence. In comparison with normal group, there were statistical difference in age, T staging, N staging, and clinical staging (P<0.0001). In survival analysis, in comparison with under-weight group, we could found the hazard ratio was less than one, in the risk of death, cancer recurrence and local recurrence. Meanwhile, the hazard ratio gradually declined when the body weight increased. In univariate survival analysis, under-weight patient had a significant decrease in overall survival,(P<0.0001). When Cox regression model was applied to multivariate analysis, we could found age, T staging, N staging, and BMI grades could be a significant independent prognosis factors(P<0.05). Under-weight patients had a significant decrease in overall survival rate, distant metastasis failure-free survival, and local relapse-free survival. Pretherapy BMI grades could be a significant independent prognosis factors.