The study aimed to investigate and compare some characteristics of Bombyx mori and Eri (Philosamia ricini) silks in different forms; with and without sericin. The protein contents were measured and find out the composition of the silk fibroin and sericin proteins by Lowry method. The secondary structure and thermal behavior of all kind of silk were determined by FT-IR and TA instrument, respectively. The B. mori composed of more amount of sericin content than that of Eri silk. FT-IR spectra indicated that the Eri silk was similar profile of silk with and without sericin, whereas B. mori silk showed dramatically differed. With sericin, B. mori composed of higher ratio random coil and α-helix structures than β-structure. With thermogravimetric analysis, bofhS. mori and Eri silk fibers without sericin showed higher stability than that silk fiber with sericin. This is due to the crystalline region of hydrophobic amino acid composed in the fibroin core protein. The differential scanning calorimetry thermogram of B. mori was differed from Eri silk fiber. It is a promising that characteristics of the silk were influenced by both silk components and silk varieties. © 2009 Asian Network for Scientific Information.