A metallo‐supramolecular polymer poly{4‐(((3,4‐dihydroxyphenyl)(6‐oxidodibenzo[c,e][1,2]oxaphosphinin‐6‐yl)methyl)amino)phenyl‐2,2‐dimethylbutanoate} (HP) is synthesized through a Kabachnik–Fields reaction. Then HP is coated on the surface of β‐FeOOH by coordination interaction to generate organic–inorganic hybrid β‐FeOOH@HP (Fe@P) nanorods, which are used for preparing flame retardant epoxy resin (EP) nanocomposites. The structure of HP is characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy, the morphology and composition of β‐FeOOH and Fe@P nanorods are also studied by scanning electron micrograph and transmission electron microscope instruments. With the presence of 2 wt% of Fe@P, the limiting oxygen index value of EP nanocomposite increased to 32.8% with UL‐94 vertical burning V‐1 rating, and 31.4% of flexural strength enhancement, indicating the improvement of both flame retardant and mechanical properties with low loading amount. The reduction of total smoke production, average CO and CO 2 yield for EP nanocomposites with 0.5 wt% of Fe@P reflected the good smoke suppression. The flame retardant mechanism of Fe@P is also discussed.