Diabetes mellitus (DM) has become one of the most challenging public health problems globally. The increasing prevalence and mortality rates call for more effective therapeutic agents, especially for DM complications. Traditional herbs have a long clinical application history for DM treatment. Puerarin is a natural isoflavone from Pueraria lobata (Wild.) Ohwi which has been consumed both as a functional food and herb in Eastern Asia countries. Documented data has shown that puerarin has cardio-protective, neuroprotective, anti-oxidative, anti-inflammatory and many other effects. In this review, we will summarize the beneficial effects and underlying mechanisms of puerarin on DM and complications. Puerarin may directly benefit DM by decreasing blood glucose levels, improving insulin resistance, protecting islets, inhibiting inflammation, decreasing oxidative stress and inhibiting Maillard reaction and advanced glycation end products (AGEs) formation. Furthermore, puerarin may also benefit DM indirectly by retarding and improving a series of DM complications, such as cardiovascular complications, diabetic nephropathy, diabetic retinopathy, diabetic neuropathy, etc. However, comprehensive studies of its effect and mechanisms are needed. In addition, its efficacy is relatively low, which is partially due to its pharmacokinetics profiles. Though puerarin shows low toxicity to experimental animals, its safety on human remains to be clarified. Collectively, we suggest that puerarin might be a potential adjuvant agent for the treatment of DM and DM complications in future.