Aberrant activation of the NLRP3 inflammasome has been implicated in the occurrence and development of many inflammatory diseases, and thus potent inhibitors of the NLRP3 inflammasome should be explored. An antitumor agent, Leukadherin-1 (LA-1), tested in phase 1/2 clinical trials, has been reported to exert anti-inflammatory properties by blocking the NF-κB pathway. However, the effects of LA-1 on the NLRP3 inflammasome have not been conclusively determined. In this study, we found that at lower doses (below 1 μM) ex vivo, LA-1 blocked NLRP3 inflammasome activation without affecting NF-κB signaling. Accordingly, 1 mg/Kg LA-1 strongly inhibited the release of NLRP3-dependent cytokine, but only slightly inhibited NLRP3-independent-cytokines secretion in endotoxemia and alleviated NLRP3-dependent peritonitis in vivo. Mechanistically, LA-1 had no effects on ion flux or mitochondrial injury. Instead, it inhibited NLRP3 inflammasome assembly by suppressing ASC oligomerization, blocking NLRP3 self-assembly, and reducing interactions of NLRP3 with ASC and NEK7. Therefore, LA-1 inhibits NLRP3 inflammasome activation, implying that it is a potential treatment option for NLRP3-associated diseases.