The progression to type 2 diabetes mellitus (DM) and other long-term cardiometabolic risks in Chinese women with prior history of gestational diabetes (GD) was studied at 15 years postpartum. 139 Chinese women (45 with GD and 94 with normal glucose tolerance (NGT) at the index pregnancy) who had their insulin sensitivity and β-cell functions examined at 8 years postpartum were again followed up at 15 years for the investigation of the rate of type 2 DM, hypertension and metabolic syndrome. Women with prior history of GD had a significantly higher rate of hypertension (35.6% vs. 16.0%, p = 0.01), type 2 DM (24.4% vs. 5.3%, p < 0.001) and impaired glucose regulation (26.6% vs. 14.9%, p < 0.001) than women with NGT during the index pregnancy. The Matsuda insulin sensitivity index and the quantitative insulin sensitivity check index at 8 years postpartum were independent predictors of both DM and metabolic syndrome at 15 years postpartum. The conversion rate of type 2 DM increased at an average rate of 1.6% per year after a pregnancy affected by GD. Insulin resistance at 8 years postpartum could refine a future diabetic risk in women with prior history of GD.