Abstract: Cancer is a disease with the highest mortality rate in the world, developing new cancer drugs is also a very exploratory research. In this paper, spindle-shaped iron hydroxyl oxide (FeOOH NPs) was firstly prepared as a nanocarrier to polymerise pyrrole (Py) to get iron hydroxyl oxide @polypyrrole (FeOOH@PPy) composite nano-material. The structure and properties of FeOOH@PPy were characterized by FTIR, DLS, TEM and UV-vis, etc. The photothermal conversion experiments proved that the composite nanoparticles had excellent photothermal conversion properties, and the biocompatibility and application potential of the composite nanomaterial in tumor therapy were explored. The results show that the average particle size of the obtained nanoparticles is about 100 nm, and has good stability in the aqueous solution. The results of the photothermal performance test show that FeOOH@PPy composite nanoparticles can absorb 808 nm near-infrared light and convert it into enough heattotrigger the apoptosis of tumor cells. In a 14 days treatment on 4T1 breast cancer mouse model, FeOOH@PPy composite nanoparticles show excellent antitumor effect. Tissue analysis show that the composite nanoparticles have no significant effect on normal tissues of mice, suggesting that the composite nanoparticles have the potential as photothermal therapy agent.