Objective: This study was retrospectively evaluated the outcome of postoperative intensity modulation radiotherapy (IMRT) for patients with adenoid cystic carcinoma of head and neck (ACCHN), and identified the unfavorable prognostic factors. Methods: Fifty-five ACCHN patients treated in Sichuan Cancer Hospital between January 2007 and December 2016 were retrospectively evaluated. Median age of patient was 47 years (range, 21-73 years). Thirty-five patients were male and 20 were female. In 30 patients, tumors were located in major salivary glands (54.5%), and 25 patients in minor salivary glands (45.5%). The numbers of R0, R1, and R2 surgical resection classification patients were 22 (40.0%), 20 (36.4%), and 13 (23.6%). The median total RT dose was 62 Gy (range, 46-72 Gy), and 54.5% of patients were treated with adjuvant chemotherapy. Statistical analyses were performed using the Log rank test for univariate analysis and the Cox proportional hazard model for multivariate analysis. Results: Median follow-up period was 68.5 months (12-132 months). The 5-year local-regional recurrence-free survival (LRRFS), distant metastasis-free survival (DMFS) and overall survival (OS) were 93.9%, 75.3% and 82.5%. In univariate analysis, T stages (p=0.025) and AJCC stages (p=0.036) were the prognostic factors for OS; Age (p=0.042), T stages (p=0.025), N stages (p=0.021), AJCC stages (p=0.021) and adjuvant chemotherapy (p=0.010) were the prognostic factors for DMFS; T stage (p=0.049) was the prognostic factor for LRRFS. In multivariate factors analyses, T stages (p=0.026), AJCC stages (p=0.028) and RT dose (p=0.025) were the significant prognosticators for OS. The most common acute toxicities over three degrees were myelosuppression (5.5%), mucositis (9.1%) and dermatitis (1.8%). Conclusion: Postoperative IMRT seems to achieve reasonable local-regional control and OS in patients with adenoid cystic carcinoma of head and neck, with acceptable treatment relative toxicities.