Native structure and degradation pattern of silk sericin were investigated by solution and solid-state NMR analyses using a fibroin-deficient silkworm strain "Sericin Hope". Two major conclusions could be drawn: 1) Sericin forms a largely random coil structure in the native state and undergoes no remarkable structural changes during spinning. 2) Asp residues periodically contained in the repeated region of sericin might be a weak point toward hydrolysis by heat treatment. In addition, sericin materials with practical mechanical strength such as film, hydrogel, and porous sponge could be prepared by utilizing non-degraded sericin obtained from the cocoon shell of Sericin Hope silkworm.