Prolactin plays an important role in maintaining a normal glucose homeostasis during pregnancy and beyond. Studies investigating the association between prolactin and type 2 diabetes beyond pregnancy are rare and none is prospective. We aimed to examine whether prolactin associates with type 2 diabetes prospectively in a Chinese population. In 2009, 2,377 participants aged 40 years or older were enrolled from Shanghai, China. Among 1,596 diabetes-free participants at baseline, 1,510 completed the follow-up investigation in 2013. Participants who had a fasting plasma glucose ≥126 mg/dL and/or a 2-hour plasma glucose ≥200 mg/dL during a 75-g oral glucose tolerance test had a definite diagnosis of type 2 diabetes or received antidiabetic therapies during follow-up were classified as having type 2 diabetes. During a mean follow-up of 3.7 years, 189 new cases of type 2 diabetes were documented. After multivariate adjustment, women in the highest quartile of prolactin showed the lowest risk for diabetes compared with those in the lowest quartile (hazard ratio = 0.48, 95% confidence interval: 0.26, 0.90). However, such significant associations were not observed in men. Prolactin may be a mediator in the pathogenesis of type 2 diabetes in women; however, more studies are needed to elucidate the underlying sex-specific mechanism.