Based on sex-inheritance of the striped Bombyx moli the females of sex-limited strain 2032 were used to hybridize with the males of natural mutants. As there was separation from F₂ generation, all black marking silkworms were discarded, and the normal and the plain marking silkworms were reserved, so as to obtain the new sex-limited normal marking strain．Then systematic selection and breeding were conducted for three generations, in which F₃ was mixed rearing and F₄～F₅ was individual rearing．It was emphasized individual selection for mixed rearing and it was mainly interbatch selection and subsequently individual selection in individual rearing. After the traits became stabilized, the economic traits were measured. The results showed that the duration of the 5th instar and all instars of new sex-limited strain was slightly shorter than those of the parents. The weight of whole cocoon, amount of cocoon shell, and rate of cocoon shell of new sex-limited strain was improved 31%, 38%, and 5%, respectively, than those of the parents.