To fabricate biocompatible composite films with tunable performance, both silk fibroin (SF, -crystallite rich) and keratin (-helix rich) materials are engineered at the mesoscale based on the molecular synergy. While SF materials display a hierarchical structure initiated from the -crystallite molecular networks, keratin materials reveal the networks crossly linked by disulfide bonding. It is surprising to see that the -crystallites of SF materials induce the conversion of the free unfolded molecular chains of keratin to -folding (-crystallites) in the SF/keratin composites. Furthermore, the -helices from the keratin components in the SF/keratin composites can transit to -sheets under stress, which gives rise to the strain-hardening, and a better flexibility and elasticity. It follows that the tensile and biodegradable performance of the SF/keratin composites can be programmed by adjusting the ratio of SF versus keratin in the composites. Raising the SF ratio in the composite films increases the density of -crystallites in the networks, giving rise to the enhanced toughness and reduced biodegradation rate, but poor deformation recovery. On the other hand, increasing the ratio of keratin in the composite films increases the extensibility, strain-hardening effect. These make them excel bio-optical materials with controllable properties.