A BmSG-SWUl cell line was established from the silk gland tissues of newly hatched Bombyx mori L. larvae by performing primary cultures for 2 yr. The cell line was comprised of long and thin shuttle cells. The percentage of cells with the chromosome number 2n = 56 was 76.28%. Therefore, the cell line was considered a diploid cell line. Fingerprint analysis of BmSG-SWUl cells and four other cell lines indicated that BmSG-SWUl cells had a specific fingerprint, and that the genetic relationship between BmSG-SWUl cells and the original silk gland tissue was the closest. We used whole genome microarray data, reverse transcription-polymerase chain reaction and fluores cence quantitative real-time-polymerase chain reaction to analyze the expression profile of BmSG-SWUl cells. On day 3 of the fifth instar silk gland, the two known silk gland-specific genes Fib-L and P25 as well as 18 other highly expressed genes were found in the whole genome microarray data. Only some of these were expressed in the BmSG-SWUl cell line, which showed that this cell line had maintained some gene expression characteristics of silk gland. The key cell cycle-control genes BmCyclinB and BmCyclinB3 of the G2 and M phase were expressed at low levels in silk glands. Contrarily, they were highly expressed in BmSG-SWUl cells, in the ovaries and other cell lines, which suggested that BmCyclinB and BmCyclinB3 are important for the transformation of BmSG-SWUl cell line from endoreduplication to the mitotic cycle.KEY WORDS Bombyx mori, silk gland, cell line, gene expression Materials and MethodsBombyx mori, Xiafang X Qiubai (XQ) samples were provided by the Silkworm Genetic Resource