Objective:To investigate the regulatory effect of deoxycytidine kinase (dCK) on ionizing radiation (IR) induced ferroptosis in triple-negative breast cancer (TNBC).Methods:TNBC cell line MDA-MB-231 was used to establish dCK knockdown and different phosphorylation phenotypes cell models, and were treated with ferroptosis activator Erastin and / or ferroptosis inhibitor ferrostatin-1 (Fer-1) combined with / without X-ray irradiation. Cell viability was detected by MTT assay. The level of reactive oxygen species (ROS) was measured by 2′,7′-dichlorofluorescin diacetate (DCFH-DA) staining. The expression levels of dCK, transferrin, transferrin receptor (TfR1), ferroportin (FPN) and ferritin heavy chain 1 (FTH1) were detected by Western blot. Statistical analysis was performed by SPSS 17.0 and Origin 2021 software. Measurement data with normal distribution were expressed by Mean ±SD. The comparison between two groups was conducted by Student t-test. The comparison among three or more groups was performed by one-way analysis of variance. Results:In MDA-MB-231 cells, IR induced cell death was observed and Erastin significantly promoted radiation induced cell death, while Fer-1 was able to reverse radiation induced cell death. Compared with the control group, IR induced cell death was increased, the level of ROS was suppressed in the dCK knockdown group. Erastin combined with IR induced reduced cell death and weakened ROS level. Fer-1 reduced the degree of IR induced cell death, and it could not inhibit the induction of ROS by IR.Compared with the control cells, the rate of cell death was decreased induced by IR, the level of ROS was decreased, the expression of FTH1 was down-regulated after IR in the dCK wild-type (dCK-WT ) or dCK hyperphosphorylated (dCK-S74E) MDA-MB-231 cells. In addition, Erastin promotes IR induced cell death and increased ROS levels, while Fer-1 significantly enhances the degree of reversal of IR induced ROS and cell death in these cells. Conclusions:dCK phosphorylation increases ferroptosis induced by IR in TNBC cells. Targeting dCK may be a novel therapeutic approach to overcome radioresistance in TNBC treatment.