HOIPIN-8 is a novel potent and selective inhibitor of linear ubiquitin chain assembly complex (LUBAC). HOIPIN-?8 suppressed the linear ubiquitination activity by recombinant LUBAC at an IC50 value of 11 nM, corresponding to a 255-?fold increase over that of HOIPIN-?1. Furthermore, as compared with HOIPIN-?1, HOIPIN-?8 showed 10-?fold and 4-?fold enhanced inhibitory activities on LUBAC- and TNF-?α-?induced NF-?κB activation respectively, without cytotoxicity. These results indicated that HOIPIN-?8 is a powerful tool to explore the physiological functions of LUBAC.