H₂S is a gaseous signaling molecule that modifies cysteine residues in proteins to form persulfides (P‐SSH). One family of proteins modified by H₂S are zinc finger (ZF) proteins, which contain multiple zinc‐coordinating cysteine residues. Herein, we report the reactivity of H₂S with a ZF protein called tristetraprolin (TTP). Rapid persulfidation leading to complete thiol oxidation of TTP mediated by H₂S was observed by low‐temperature ESI‐MS and fluorescence spectroscopy. Persulfidation of TTP required O₂ , which reacts with H₂S to form superoxide, as detected by ESI‐MS, a hydroethidine fluorescence assay, and EPR spin trapping. H₂S was observed to inhibit TTP function (binding to TNFα mRNA) by an in vitro fluorescence anisotropy assay and to modulate TNFα in vivo. H₂S was unreactive towards TTP when the protein was bound to RNA, thus suggesting a protective effect of RNA.