The aim of this study was to evaluate changes in lipid profiles in patients with type 2 diabetes after treatment conversion from rosiglitazone to pioglitazone while maintaining stable statin and other lipid-altering therapies. A total of 305 patients were enrolled in this open-label study. Patients had been taking stable dosages of rosiglitazone and statins for > 90 days. At baseline, patients discontinued rosiglitazone and started pioglitazone 30 mg/day, but continued statins and other lipid-altering therapies. The primary end point was change from baseline in fasting triglyceride levels. At 17 weeks after treatment conversion, patients had significant reductions in triglycerides (-15.2%), total cholesterol (-9.0%), and low-density lipoprotein (LDL) particle concentration (-189 nmol/L), and increases in LDL cholesterol (+2.2%), high-density lipoprotein (HDL) cholesterol (+1.8%), and LDL particle diameter (+0.23 nm). In conclusion, after treatment conversion from rosiglitazone to pioglitazone while maintaining stable statin therapy, patients with type 2 diabetes had marked improvements in lipid profiles along with stable glycaemic control.