Significance Wnt proteins signal through frizzled (FZD) receptors to regulate physiological processes; however, the structural basis for recognition of the Wnt unsaturated fatty acyl group by FZDs remains elusive. Here, we report the first structures of the extracellular cysteine-rich domain (CRD) of two members of the FZD family in complex with free fatty acids. We show that the fatty acid bridges two CRD molecules and occupies the lipid-binding groove, which adopts a U-shaped geometry and exhibits flexibility. Our findings suggest a common mechanism for fatty acyl recognition by multiple FZD receptors and imply that Wnt binding to FZD mediates its dimerization. Overall, this study provides structural insights into how cell-surface FZD receptors recognize cis -unsaturated fatty acyl groups on Wnt ligands.