The differences of protein expression between the improved cross breeding race Jinqiu and its parents were analyzed to discuss the gene construction.and to form a base for illuminating the molecular mechanisms of successful cross breeding in silkworm.Protein samples from silk gland,hemolymph,and midgut were separated by 2-dimensional gel electrophoresis (2-DE).In the three tissues the matched protein spots between Jinqiu and its cross parents were approximately 70% with approximately 30% specific protein spots.In the matched protein spots,9-24% was differentially expressed representing up-and down-regulated expression.These specific protein spots might be either the newly appeared,which were produced from the genie interaction of cross parentsgenes in cross breeding,or posttranscriptionally modified,which were produced from che different modifications on the same original proteins.These results indicate that it is important for a new successful breed,by cross breeding,relying on the actions of some newly produced functional proteins from genic interaction,in addition to marshaling excellent genes of cross parents.