Silk proteins and silk fibers from silkworm (Bombyx mori L.) cocoons were partially hydrolyzed by acids, and the cleaved peptide mass fragments (PMFs) were analyzed using matrix-assisted laser desorption/ionization time-offlight mass spectrometry (MALDI-TOF MS). Cleaved PMFs obtained via MALDI-TOF MS analysis were compared among 34 local silkworm race cocoons. Dendrograms were created based on the cleaved PMFs of raw, heat-treated, sodium carbonate-treated, Marseille soap-treated, and hydrogen peroxide-treated silk fibers against Marseille soap-treated silk fibers. The identified differences suggested that it was possible to distinguish between races of silkworm cocoons and fibers based on the cleaved PMFs.