Theeffectof treatmentwithX- andgamma rayson themajor quantitative characteristics determining the productivity of cocoons and rawsilk at different development stages of Bombyx mori L. was an object of studies by many authors. The aim of the present investigation was the use of low doses of gamma rays and analysis of the genetic effect on the filamentlength after the crossing and individual females treated and untreatedwith gamma raysin the process of establishing newlines of silkworms of the Chinese type. The analysis for establishing the genetic effects on crossings between treated males and untreated females and vice versawas madewith the specialized software ofJochen Wolf (1996). Apositive statistically significant genetic effect on the filament lengthwas established after crossing treated and untreated genetic groups of males and females. A positive heterosis effect was found, the strongest one being reported in the genetic group c22 – 65.40.