Background One of the therapies used to treat type 2 diabetes mellitus (T2DM) disease is combination insulin which consists of rapid-acting insulin and intermediate-acting insulin (premixed). This study aimed to examine the profile of premixed insulin related to blood glucose concentration and to identify the drug interactions due to the combination of premixed insulin with other drugs taken by T2DM patients. Methods This study was a prospective observational study with cross-sectional data that were analyzed descriptively. The respondents invited were T2DM patients with or without complication or comorbid disease who received premixed insulin with or without a combination of oral antidiabetic therapy in the Outpatient Unit of Universitas Airlangga Hospital, Surabaya. The research instruments used are data sheet, patient medical record, and fasting and postprandial blood glucose concentration. Results A total of 118 patients received premixed insulin therapy, but only 80 patients were included in the inclusion criteria. Based on types of insulin, the combination of 30% aspart and 70% protamine aspart was used by 91.25% T2DM patients, and a combination of 25% insulin lispro and 75% protamine lispro was used by 8.75% T2DM patients. There were 30.3% of patients who could achieve the target of 80-130 mg/dL in fasting blood glucose concentrations, and 35.1% of patients achieved the target of ≤180 mg/dL in postprandial blood glucose concentration. Drug interactions may occur in patients who use premixed insulin with glimepiride, lisinopril, fenofibrate, candesartan, irbesartan, and gemfibrozil. Conclusions In this study, premixed insulin have not reached the target of fasting and postprandial blood glucose concentrations in most patients.