As the most promising anode material for next-generation Li batteries, Li metal never loses the academic attention due to its inherent superiority in high theoretical capacity and low redox potential. However, Li dendrites formed during cycling stubbornly hinder the pace of commercializing high-energy-density Li metal batteries. Here sericin endowed with abundant lithiophilic and anionphilic functional groups on its polypeptide chain is proposed as a conformal protective coating on both Cu and Li metal anodes. The resulting increase of Li-ion transference number (as high as 0.876) and mitigation of tip effect are favorable for the homogeneous Li deposition in island-like or lateral growth mode at electrode/electrolyte interface. Long cycle life (335 cycles) and high Coulombic efficiency (98%) are obtained in sericin decorated Li/Cu cells. Even under extremely high current density of 10 mA cm−2 based on a large capacity of 5 mAh cm−2, the sericin decorated Li anode also enables a superior cycle stability (160 cycles) in the symmetric cells. The conformal sericin coating effectively inhibits the corrosion of air to Li metal. Sericin modified Li-S batteries exhibit greatly enhanced rate performance (452.8 mAh g−1 at 5 C) and cycling performance (667.8 mAh g−1 after 520 cycles at 1 C).