The fact that we found out tissue specific expression regulation mechanism of a gene is important to understand development and cell differentiation mechanism. The transcription of fibroin gene occur only at the posterior silk gland. Particularly, it is expressed ver strongly at the latest age of the fifth instar, and produces fibroin that accounts for about 20% of the body weight. Like above, it is supposed to provide a significant clue for the study of genetic expression regulation mechanism to explain a strong tissue-specific expression regulation mechanism of fibroin. The firefly luciferase gene was used as a reporter of gene expression. The pLuc vector was microinjected into the fertilized eggs and we had transgenic silk worms. Hatching rate is about 1%. We have resolved the generation of F1 by Luciferase assay. Consequently, we have found out that the firefly luciferase gene was expressed up to progeny. In addition, we gained transformants in terms of inserting pFPLuc vector containing fibroin light chain promoter by using microinjection which has already been resolved. We are analyzing in order to examine the degree of the activation of fibroin promoter. It is expected that the results make it possible to study the strong promoter and production of the useful substances in eukaryotes.