〔Abstract〕 To investigate the role of STAT3 phosphorylation in ferroptosis regulation and its impact on cisplatin resistance mechanisms in human osteosarcoma cells．Methods Human osteosarcoma HOS cells and cispl- atin-resistant HOS / DDP cells were treated with cisplatin ( 0. 5，1，2，4，8，16，32 mg / L) ，the ferroptosis inducer Erastin ( Era) ( 2 μmol / L) ，and / or the ferroptosis inhibitor Ferrostatin-1 ( Fer1) ( 10 μmol / L) ．Cell viability and proliferation were assessed using the Cell Counting Kit-8 ( CCK-8) and colony formation assays，and cell migration was evaluated via a scratch assay．Reactive oxygen species ( ROS) ，intracellular ferrous iron levels，mitochondrial membrane potential，mitochondrial function，malondialdehyde ( MDA) levels，and the reduced glutathione / oxi- dized glutathione ( GSH / GSSG) ratio were measured using commercial kits．The mRNA expression of ferroptosis- related genes was analyzed by quantitative reverse transcription polymerase chain reaction ( RT-qPCR) ．The protein levels of glutathione peroxidase 4 ( GPX4) ，solute carrier family 7 member 11 ( SLC7A11) ，phosphorylated STAT3 ( p-STAT3) ，and total STAT3 were determined by Western blot．Results With cisplatin treatment，HOS cells ex- hibited decreased cell viability，mitochondrial membrane potential，and GSH / GSSG ratio ( P＜0. 01) ，along with elevated levels of ROS，ferrous ion，and MDA content ( P ＜0. 01) ． The protein levels of GPX4 ( P ＜0. 01) ， SLC7A11，and p-STAT3 also decreased ( P ＜0. 05) ．Coadministration with the ferroptosis inhibitor Ferrostatin-1 ( Fer-1) reversed these aforementioned effects ( P ＜0. 05) ．In HOS / DDP cells，the mRNA levels of ferroptosis- suppressive genes ( GPX4，FTH1，SLC7A11，and AIFM2) were significantly higher than those in HOS cells ( P < 0. 05) ，whereas the expression of ferroptosis-promoting genes ( ACSL4 and PTGS2) was significantly lower ( P < 0. 05) ．The cisplatin-induced reductions in cell viability and mitochondrial membrane potential，as well as the in- creases in ROS，ferrous ion，and MDA levels，were less pronounced in HOS / DDP cells than in HOS cells．The SLC7A11 protein level showed no significant change． However，combined treatment with the ferroptosis inducer Erastin ( Era) resulted in significant decreases in viability，mitochondrial membrane potential，and the GSH / GSSG ratio in HOS / DDP cells ( P＜0. 05) ．Furthermore，the protein levels of p-STAT3，GPX4，and SLC7A11 were also markedly reduced ( P＜0. 05) ．Conclusion The activation of ferroptosis mediated by p-STAT3 enhances cisplatin sensitivity in HOS / DDP cells．