Background <p>Microsatellite instable (MSI) colorectal cancer (CRC) has distinct features that distinguish it from microsatellite stable CRC. While ferroptosis may play a role in the development of MSI CRC, its mechanisms remain unclear.</p> Methods <p>Ferroptosis was assessed via the detection of lipid peroxidation, malondialdehyde, 4-hydroxy-2-nonenal, and intracellular Fe2⁺, etc. Phosphoproteomic analysis, cytokine array, and flow cytometry were performed to explore the regulation of CD8⁺ T cell infiltration.</p> Results <p>Dual specificity phosphatase 4 (DUSP4) suppressed ferroptosis in MSI CRC cells by reducing lipid peroxidation and inhibiting intracellular Fe2⁺ accumulation. Mechanistic studies showed that DUSP4 downregulated the expression of transferrin receptor (<i>TFRC</i>), which was transcriptionally regulated by c-MYC. In addition, a positive correlation was observed between the infiltration of CD8⁺ T cells in CRC tissues and the expression of <i>DUSP4</i> in cancer cells. Mechanistically, DUSP4 dephosphorylated cyclin-dependent kinase 7 (CDK7) and promoted C-X-C Motif chemokine ligand 16 (<i>CXCL16</i>) expression, resulting in an increased infiltration of CD8⁺ T cells. Importantly, the combination of a CDK7 inhibitor and anti-programmed cell death protein-1 therapy demonstrated a synergistic therapeutic effect in MSI CRC.</p> Conclusion <p>DUSP4 acts as a negative regulator of ferroptosis and a positive regulator of CD8⁺ T cell infiltration in MSI CRC.</p>