WD-repeat proteins are very diverse, yet these are structurally related proteins that participate in a wide range of cellular functions. WDR13, a member of this family, is conserved from fishes to humans and localizes into the nucleus. To understand the in vivo function(s) of Wdr13 gene, we have created and characterized a mutant mouse strain lacking this gene. The mutant mice had higher serum insulin levels and increased pancreatic islet mass as a result of the enhanced beta cell proliferation. While a known cell cycle inhibitor, p21, was down regulated in the mutant islets overexpression of WDR13 in the pancreatic MIN6 cell line resulted in upregulation of p21, accompanied by retardation of cell proliferation. We suggest that WDR13 is a novel negative regulator of the pancreatic beta cell proliferation. Co-immunoprecipitation experiments showed that this protein interacts with estrogen receptors and various HDACs. We provide evidence to show that WDR13 can regulate estrogen receptors-mediated transcription both in HDAC-dependent and HDAC-independent manner. Given the higher insulin levels, better glucose clearance and the lack of insulin resistance in WDR13 deficient mice, we propose that this protein may be a potential candidate drug target for ameliorating impaired glucose metabolism in diabetes.