Although recent studies recommended that insulin should be administered to patients with slowly progressive type 1 diabetes, even those with non-insulin dependent status, patients prefer oral hypoglycemic agents to insulin injections. We report a slowly progressive type 1 diabetic patient whose insulin production was preserved for 4 years (SigmaC-peptide from 29.48 ng/mL to 24.58 ng/mL) using pioglitazone despite a high titer of anti-GAD antibody (GADA; 120.7 U/mL). This case suggests that pioglitazone might prevent or delay the loss of insulin secretion and insulin dependency in slowly progressive type 1 diabetic patients.