Angiopoietin-like 4 (ANGPTL4) is a secreted signaling protein that is implicated in cardiovascular disease, metabolic disorder, and cancer. Outside of its role in lipid metabolism, ANGPTL4 signaling remains poorly understood. Here, we identify ANGPTL4 as a Wnt signaling antagonist that binds to syndecans and forms a ternary complex with the Wnt co-receptor Lipoprotein receptor-related protein 6 (LRP6). This protein complex is internalized via clathrin-mediated endocytosis and degraded in lysosomes, leading to attenuation ofWnt/b-catenin signaling. Angptl4 is expressed in the Spemann organizer of Xenopus embryos and acts as a Wnt antagonist to promote notochord formation and prevent muscle differentiation. This unexpected function ofANGPTL4 invites reinterpretation of its diverse physiological effects in light of Wnt signaling and may open therapeutic avenues for human disease.