Cellular FLICE-inhibitory protein (c-FLIP) is an inhibitor of caspase-8 and is required for macrophage survival. Recent studies have revealed a selective role of caspase-8 in noncanonical IL-1b production that is independent of caspase-1 or inflammasome. Here we demonstrated that c-FLIP L is an unexpected contributor to canonical inflammasome activation for the generation of caspase-1 and active IL-1b. Hemizygotic deletion of c-FLIP impaired ATP-and monosodium uric acid (MSU)-induced IL-1b production in macrophages primed through Toll-like receptors (TLRs). Decreased IL-1b expression was attributed to a reduced activation of caspase-1 in c-FLIP hemizygotic cells. In contrast, the production of TNF-a was not affected by downregulation in c-FLIP. c-FLIP L interacted with NLRP3 or procaspase-1. c-FLIP is required for the full NLRP3 inflammasome assembly and NLRP3 mitochondrial localization, and c-FLIP is associated with NLRP3 inflammasome. c-FLIP downregulation also reduced AIM2 inflammasome activation. In contrast, c-FLIP inhibited SMAC mimetic-, FasL-, or Dectin-1-induced IL-1b generation that is caspase-8-mediated. Our results demonstrate a prominent role of c-FLIP L in the optimal activation of the NLRP3 and AIM2 inflammasomes, and suggest that c-FLIP could be a valid target for treatment of inflammatory diseases caused by overactivation of inflammasomes.