The research was carried out in the laboratory of genetics and breeding of the silkworm of the Research Institute of Sericulture between 2008 and 2011. The starting material used in high-yield breeding lines 4, with thin cocoon thread. To saturate the genome krupnokokonnyh Line 48, Line 51 genes tonkoshelkovistyh rocks 66 Japanese, Chinese 108, carried out pairing for 4 years in the appended scheme. Double enrichment of large-sized cocoon breed of silkworm Line 48, Line 51 with genes of East-Asian tine — silk breed of Japanese-66 Chinese-108 brings to the fineness of cocoon thread. Accordingly, to improve the quality of silk thread krupnokokonnyh rocks, we recommend a two bekkrossnyh crossings with rocks-improvers. This technique can be used in industrial sericulture Uzbekistan.