Pancreatic β cell failure is a hallmark of diabetes. However, the causes of β cell failure remain incomplete. Here, we report the identification of tetranectin (TN), an adipose tissue–enriched secretory molecule, as a negative regulator of insulin secretion in β cells in diabetes. TN expression is stimulated by high glucose in adipocytes via the p38 MAPK/TXNIP/thioredoxin/OCT4 signaling pathway, and elevated serum TN levels are associated with diabetes. TN treatment greatly exacerbates hyperglycemia in mice and suppresses glucose-stimulated insulin secretion in islets. Conversely, knockout of TN or neutralization of TN function notably improves insulin secretion and glucose tolerance in high-fat diet–fed mice. Mechanistically, TN binds with high selectivity to β cells and inhibits insulin secretion by blocking L-type Ca 2+ channels. Our study uncovers an adipocyte–β cell cross-talk that contributes to β cell dysfunction in diabetes and suggests that neutralization of TN levels may provide a new treatment strategy for type 2 diabetes.