Downsizing supported metal of Fe⁰-based materials in dealing with ever-growing pharmaceutical contamination issues are highly desired but still challenging. Herein, we develop a modular design protocol to synthesize a family of ultrafine alloy nanoclusters embedded in a nitrogen-enriched carbon framework (NEC@FeM (M=Pd, Pt, Au)). Engineering the fine structure of nitrogen-enriched carbon and interfacial interaction with bimetallic nanoclusters largely suppresses bimetallic overgrowth, eventually producing supported ultrafine (< 4 nm), highly dispersed, well-alloyed nanoclusters. The alloying Fe⁰ with M for ultrafine nanoclusters optimize the electron flow, chemical stability, and catalytic property, resulting in the obtained NEC@FeM exhibiting excellent doxorubicin (DOX) degradation performance. Density functional theory calculation combined with experimental results attribute the outstanding DOX degradation ability of NEC@FePd originally to the synergistic effect of enhanced DOX affinity and efficient electrons transfer from Fe to DOX. This work provides a paradigm for the design of ultrafine Fe⁰-based nanocluster with application in pollution control.