<p>Nakajo-Nishimura syndrome/proteasome-associated autoinflammatory syndrome (NNS/PRAAS) is a hereditary autoinflammatory disease. Clinically, NNS/PRAAS is characterized by periodic fever, skin rash, partial lipo-muscular atrophy, and joint contractures. Among PRAAS, NNS, is genetically characterized by a homozygous founder variant in the <i>proteasome subunit beta type 8 (PSMB8)</i> gene encoding an inducible proteasome component β5i. To establish an in vivo animal model recapitulating NNS/PRAAS, we generated mice harboring this founder variant. In <i>Psmb8</i>^{<i>G201V/G201V</i>} mice, the immature β5i subunit was increased and 20S proteasome activity was significantly reduced in the spleen, whereas 26S proteasome activity was preserved and ubiquitin accumulation was not apparent. Compared with wild-type mice, <i>Psmb8</i>^{<i>G201V/G201V</i>} mice exhibited a shortened lifespan and, as they aged, showed less weight gain and adipocyte shrinkage with interstitial macrophage infiltration and cytokine production/activation. The mutant mice also manifested significantly lower proportion of T cells in total splenocytes, with higher CD4⁺ and lower CD8⁺ T cell proportions. <i>Psmb8</i>^{<i>G201V/G201V</i>} mice shared some characteristic autoinflammatory and progeroid phenotypes as observed in NNS/PRAAS patients, although their proteasome defect pattern was distinct. Thus, <i>Psmb8</i>^{<i>G201V/G201V</i>} mice should be useful not only for investigation of NNS/PRAAS pathogenesis but also for examining the clinical effect of candidate drugs on NNS/PRAAS and related diseases.</p>