Abstract: The cocoon filaments and degummed fibers of different breeds/hybrids of Bombyx mori Linn., viz., CSR2 and CSR4 (Pure bivoltine) CSR2 x CSR4 (Bivoltine hybrid); PM x CSR2 (Multivoltine x bivoltine hybrid) and Pure Mysore (Pure multivoltine) were examined using a scanning electron microscope. The study was under taken in order to clarify the characteristics of cocoon filament, degummed fibers and to confirm the presence of voids/striae. The morphological study reveals the presence of number of voids and variation in their shape and size at ultrastructure level. The number of voids in Pure Mysore is higher than those found in pure bivoltine and their hybrids. Further, the shape and size of these voids differ from that of the voids noticed in cross section of pure multivoltine and multi x bivoltine hybrids. The voids studied in all the breeds of B. mori were elongated in the direction of the fiber axis. Large sized and more number of voids were observed in male cocoon filament than that of female cocoon filament in all the breeds/hybrids of B. mori x bivoltine hybrids. Further, some voids were gradually flattened during the cocoon cooking and degumming process, which finally closed and transformed into striae resulting in an increased compactness of degummed fiber in all the breeds/hybrids studied.