SignificanceCytosolic lipopolysaccharides (LPSs) induce oligomerization of caspase-4/5/11, resulting in pyroptosis, but the involvement of any other host resistance factors in this process is unknown. Galectins bind to components of pathogenic microorganisms, particularly LPSs, in a glycan-dependent manner. However, these proteins are mainly present intracellularly, and little is known regarding their functions associated with binding to components of microorganisms, including LPSs, in the cytosol. Here, we report that galectin-3 recognizes cytosolic LPSs from various bacteria and amplifies LPS-induced caspase-4/11 oligomerization and activation, causing more intense pyroptosis in a carbohydrate-dependent manner. This study defines a unique molecular mechanism based on the carbohydrate-binding and self-association properties of galectin-3, through which this glycan-binding protein enhances cytosolic LPS-induced noncanonical inflammasome activation in macrophages.