In rodents, obesity and aging impair nicotinamide adenine dinucleotide (NAD+) biosynthesis, which contributes to metabolic dysfunction(1–8). Nicotinamide mononucleotide (NMN) availability is a rate-limiting factor in mammalian NAD+ biosynthesis. We conducted a 10-week, randomized, placebo-controlled, double-blind trial to evaluate the effect of NMN supplementation on metabolic function in postmenopausal women with prediabetes who were overweight or obese. Insulin-stimulated glucose disposal, assessed by using the hyperinsulinemic-euglycemic clamp, and skeletal muscle insulin signaling (phosphorylation of AKT and mTOR) increased after NMN supplementation, but did not change after placebo treatment. NMN supplementation up-regulated the expression of platelet-derived growth factor receptor β and other genes related to muscle remodeling. These results demonstrate NMN increases muscle insulin sensitivity, insulin signaling and remodeling in women with prediabetes who are overweight or obese.