This work deals with the chemical composition, physical structure, and thermal behavior of Antheraea assama silk fibers. The amino acid composition is characterized by the high content of alanine, glycine, and serine. Among the amino acid residues with polar side chains, aspartic acid, arginine, and tyrosine prevail. The birefringence and isotropic refractive index values are 0.030 and 1.557, respectively. The stress-strain curve shows a yield point at 5% elongation, followed by a region of gradual extensibility. Elongation at break is about 40%. The X-ray diffraction pattern is typical of beta silks, with - (ala)n- repeats in the polypeptide sequences of the crystalline regions. The differential scanning calorimetry curve shows two minor endotherms at 230 and 300-degrees-C, before final thermal decomposition at 362-degrees-C. The maximum extent of contraction exhibited by the thermomechanical analysis curve is 2%. The surface of degummed fibers shows the presence of longitudinal striations. The fiber cross section is mostly elliptical. Raw fibers taken from cocoons show the presence of several crystalline deposits on the surface, identified as crystals of calcium oxalate.