Inbreeding and selection were carried out conducted for 7-9 generation for the evolution of pure lines of silkworm from four hybrid populations imported from China. Two external morphological characters as the color and pattern of the larvae and shape of cocoon were taken into consideration for purification of the lines. With this method six pure lines, four of Chinese origin and two of Japanese origin, were evolved. All these lines were stable and bred true for the two characters. They were all suitable for rearing in the spring season.