Abstract: CY-1-4 is a tryptanthrin derivative exhibiting antitumor activity. The solubility of CY-1-4 was poor and the corresponding mechanism needs further study. To solve this problem, we prepared nanoparticles encapsulated with CY-1-4 (CY-1-4 NPs) by nanoprecipitation method using poly(caprolactone) (PCL) and poly(ethylene glycol)-co-poly(ε-caprolactone) (PEG-PCL) as carriers to improve solubility. We then explored whether CY-1-4 NPs induced B16-F10 cytotoxicity via ferroptosis by determining the effect of CY-1-4 NPs on reactive oxygen (ROS) levels, repairing efficacy of lipid reactive oxygen inhibitor ferrostatin-1 and iron chelator deferoxamine (DFO), and potentiation of protoporphyrin (PPIX) induced B16-F10 cell death. The results showed that nanoparticlated strategy significantly improved solubility of CY-1-4. With the particle size about 116 nm, encapsulating efficacy was about 83% and the drug loading capacity was about 4.80%. Ferroptosis mechanistic studies indicated that CY-1-4 NPs could improve the ROS level in B16-F10 cells, whereas ferrostatin-1 and DFO could partly inhibited the cytotoxicity and PPIX could potentiated the cytotoxicity of CY-1-4 NPs in B16-F10 cells. These results showed that ferroptosis was one of the cell death mechanisms induced by tryptanthrin derivative CY-1-4 nanoparticle.