Background: To determine the treatment efficacy and prognostic factors for highgrade glioma (HGG) patients treated with postoperative intensity-modulated radiotherapy (IMRT). Materials and Methods: An analysis of 86 HGG patients who underwent surgery, radiotherapy (total dose: 5460 Gy), and chemotherapy was performed retrospectively. The primary endpoint was Overall survival (OS), while the secondary endpoint was progression-free survival (PFS). Patient factors, tumor characteristics, and treatments were examined for their prognostic value. Results: Among the enrolled patients, there were 22 patients of grade III and 64 patients of grade IV. At the end of the study, 48 cases had died, and 66 cases had relapsed. The median OS was 24 months, while the median PFS was just 9 months. The mean OS of patients with grade III and IV glioma was 41 months and 16 months, respectively. Patients had relative survival rates of 73.2%, 46.6%, and 27.0% at 1, 2, and 5 years. The most common type of tumor recurrence was relapse within the radiation field. Univariate analysis indicated that sex, age, Karnofsky Performance Scale score (KPS), Pathological grade, tumor location, surgical approach, and adjuvant chemotherapy cycles were predictive factors for OS (P< 0.05). In contrast, sex, age, pathological grade, number of lesions, surgical approach, and adjuvant chemotherapy cycles were predictive factors for PFS (P < 0.05). According to multivariate analysis indicated that pathological grade, surgical approach, and adjuvant chemotherapy cycles were associated with longer OS and PFS (P< 0.05). Conclusions: Grade III gliomas, total surgical resection, and adjuvant chemotherapy for more than six cycles were associated with more favorable survival outcomes in this study.