The objective of this study was to investigate whether improving glycemic control reduces the prevalence and progression of proteinuria among bevacizumab (BEV)-treated cancer patients with type 2 diabetes mellitus (DM). We retrospectively reviewed the medical records of 55 patients with type 2 DM who were treated with BEV between July 1 2011 and May 31 2018 at Iwate Medical University Hospital. The patients were classified based on changes in glycated hemoglobin (HbA1c) level during the 3 months following BEV administration into the “HbA1c elevated” group (+0.5% or above, n =24) and the “HbA1c non-elevated” group (indicating no change or decrease; n =31). At 3 months following BEV administration, the means of HbA1c and its change rate in the ‘HbA1c elevated’ group was significantly higher than that in the ‘HbA1c non-elevated’ group, and the prevalence of proteinuria in the ‘HbA1c elevated’ group was significantly higher than that in the ‘HbA1c non-elevated’ group. Additionally, our subjects were classified into the proteinuria group and non-proteinuria group. The mean HbA1c level in the proteinuria group was significantly higher than that in the non-proteinuria group at 3 months following BEV administration. Furthermore, the mean rates of change of HbA1c level in patients experiencing grades 1 and 2 proteinuria were +9.97±2.26 and +14.0±3.82%, respectively. These values were significantly higher than those of patients with no proteinuria (−2.15±1.96%). Our results suggest that deterioration of glycemic control contributes to the prevalence of proteinuria among BEV-treated cancer patients with type 2 DM.