The treatment of prostate cancer (PCa) remains challenging, and while melatonin (MEL) has demonstrated therapeutic potential, its precise mechanisms require further elucidation. Through integrated in vitro, in vivo, and bioinformatics analyses, this study demonstrated that MEL functioned as a novel ferroptosis inducer in PCa by disrupting androgen receptor (AR) liquid-liquid phase separation (LLPS). We found that MEL effectively inhibited PCa proliferation, migration, and invasion in vitro while suppressing tumor growth safely in mice models. Mechanistically, MEL impaired AR LLPS dynamics, reducing AR-driven transcription of minichromosome maintenance protein 5 (MCM5). MCM5 was a clinically relevant biomarker associated with aggressive PCa and poor survival. Crucially, downregulated MCM5 attenuated its physical interaction with NRF2, leading to uncontrolled activation of the NRF2/HMOX1 pathway, GPX4 suppression, and accumulation of ferroptosis hallmarks. These findings defined an AR/MCM5/NRF2 axis regulating ferroptosis susceptibility, establishing MEL as the first-reported ferroptosis inducer that expands the mechanistic foundation and therapeutic potential of MEL-based PCa treatment strategies.© 2025 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.