Objective The aim of this study was to evaluate the usefulness of the modified Glasgow Prognostic Score (mGPS) as a prognostic factor in patients with non-metastatic clear cell renal cell carcinoma (RCC). Materials and methods Between June 1994 and July 2012, 469 patients with RCC underwent radical or partial nephrectomy at two hospitals. Among these patients, 65 with non-clear cell type histology and 16 with lymph-node or distant metastasis were excluded. The medical records of the remaining 388 patients were retrospectively reviewed. The mGPS was calculated using a selective combination of C-reactive protein (CRP) and albumin as previously described. The prognostic significance of various clinicopathological variables including mGPS was analyzed using univariate and multivariate analyses. Results Of the total 388 patients, 40 patients (10.3%) developed local recurrence or distant metastasis and 18 patients (4.6%) died of disease during the follow-up period. The univariate analysis identified CRP, mGPS, thrombocytosis, T stage, Fuhrman's nuclear grade and lymphovascular invasion as significant prognostic factors for recurrence-free survival (RFS) and cancer-specific survival (CSS). The multivariate analysis indicated that mGPS (p < 0.001), T stage (p = 0.024) and lymphovascular invasion (p = 0.046) were independent prognostic factors for RFS, whereas mGPS (p = 0.001) was the only independent prognostic factor for CSS. Conclusions The mGPS is an independent prognostic factor for RFS and CSS in patients with non-metastatic clear cell RCC treated with radical or partial nephrectomy. These findings suggest that mGPS should be used for predicting recurrence or survival in patients undergoing nephrectomy for non-metastatic clear cell RCC.