To product the blue fluorescent protein (AmCyan) expressed cocoon, we were fused AmCyan cDNA to the heavy chain gene and injected the gene into a silkworm. AmCyan was one of the existing violet fluorochromes and originally derived from the fluorescent protein amFP486. AmFP486 was cloned from the sea anemone Anemonia majano (GenBank accession number AF168421), and belongs to the family of fluorescent proteins (FPs) isolated from coral reef organisms. The AmCyan fusion protein, each with N- and C- terminal sequences or the fibroin H-chain, were designed to be secreted into the lumen of the posterior silk glands. The expression of the AmCyan/H-chain fusion gene was regulated by the fibroin H-chain promoter. The use of the 3xP3 EGFP as a marker allowed us to rapidly distinguish transgenic silkworm. Mixtures of the donor and helper vectors were micro-injected into 300 eggs of bivoltine silkworms (Baegokjam). EGFP fluorescence was observed in 3 broods of transgenic silkworms under a florescence stereomicroscope. The cocoon was displayed strong blue fluorescence, proving that the fusion protein was present in the cocoon. Accordingly, we suggest that the AmCyan gene expressed cocoon will be enable the production of the novel biomaterials based on the transgenic silk.