The influence of poly(asparagine-co-phenylalanine) (P(Asn-co-Phe)/SnO₂) on the protection performance of epoxy coating was investigated. The electrochemical impedance spectroscopy (EIS) analysis indicates the better protection against coating degradation of epoxy (EP)-P(Asn-co-Phe)/SnO₂ nanocomposite on tinplate compared to that of pure epoxy coatings. The coating resistance (R_coat) of the EP-P(Asn-co-Phe)/SnO₂ nanocomposite is found to be 3854.70 k？·cm². The R_coat of EP-P(Asn-co-Phe)/SnO₂ nanocomposite coating is found to be over 38 times greater than that of the EP coating. Scanning electrochemical microscopy (SECM) analysis shows less current distribution for the EP-P(Asn-co-Phe)/SnO₂. The analyses of degradation products by XRD and SEM/EDX confirm the influence of functionalized SnO₂ particles on the protecting ability of epoxy coating. The hydrophobic nature of the EP-P(Asn- co-Phe)/SnO₂ nanocomposite coating (θ=133°) is confirmed by water contact angle measurement. The resultant nanocomposite coatings display enhanced mechanical properties. The results show that the EP-P(Asn-co-Phe)/SnO₂ nanocomposite in wells increased the antibacterial activity as compared with pure EP. Therefore, it is concluded that the newly synthesized EP-P(Asn-co-Phe)/SnO₂ nanocomposite provides an outstanding barrier and mechanical properties due to the addition of P(Asn-co-Phe)/SnO₂ nanoparticles to the epoxy matrix, which obstructs the degradation of materials and assists in prolonging the life of the coated steel.