Aims To compare risks of early postpartum diabetes and prediabetes in Chinese women with and without gestational diabetes mellitus (GDM) during pregnancy. Subjects and methods Tianjin GDM observational study included 1263 women with a history of GDM and 705 women without GDM who participated in the urban GDM universal screening survey by using World Health Organization’s criteria. Postpartum diabetes and prediabetes were identified after a standard oral glucose tolerance test. Cox proportional hazards regression was used to assess risks of postpartum diabetes and prediabetes between women with and without GDM. Results During a mean follow-up of 3.53 years postpartum, 90 incident cases of diabetes and 599 incident cases of prediabetes were identified. Multivariable-adjusted hazard ratios among women with prior GDM, compared with those without it, were 76.1 (95% CI: 23.6–246) for diabetes and 25.4 (95% CI: 18.2–35.3) for prediabetes. When the mean follow-up extended to 4.40 years, 121 diabetes and 616 prediabetes cases were identified. Women with prior GDM had a 13.0-fold multivariable-adjusted risk (95% CI: 5.54-30.6) for diabetes and 2.15-fold risk (95% CI: 1.76-2.62) for prediabetes compared with women without GDM. The positive associations between GDM and the risks of postpartum diabetes and prediabetes were significant and persistent when stratified by younger and older than 30 years at delivery and normal weight and overweight participants. Conclusions The present study indicated that women with prior GDM had significantly increased risks for postpartum diabetes and prediabetes, with the highest risk at the first 3–4 years after delivery, compared with those without GDM.