Polybiquitinylation designates proteins for proteasomal degradation. USP14 is one of several deubiquitinating enzymes (DUBs) responsible for shortening proteasome-bound ubiquitin chains, which is known to antagonize the degradation of ubiquitin-protein conjugates. IU1 is a reversible, small molecule inhibitor of deubiquitination by USP14 that demonstrates an IC50 value of 4-5 μM. IU1 selectively stimulates ubiquitin-dependent protein degradation in vitro at 34 μM and in MEF cells at 50 μM. At 75 μM, IU1 reduces accumulation of oxidized proteins in HEK293 cells, alleviating cytotoxicity induced by oxidative stress.