Abstract: | Overproduction of superoxide anion (O2.?), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O2.? to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H2S). Termed SOPD‐NAC , this persulfide donor reacts specifically with O2.?, decomposing to generate N‐acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self‐assembling peptide (Bz‐CFFE‐NH2) to make a superoxide‐responsive, persulfide‐donating peptide ( SOPD‐Pep ). Both SOPD‐NAC and SOPD‐Pep delivered persulfides/H2S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD‐Pep mitigated toxicity induced by phorbol 12‐myristate 13‐acetate (PMA) more effectively than SOPD‐NAC and several control compounds, including common H2S donors. |