Ubiquitin can be covalently attached to cellular proteins as a post-translational modification rind is involved in metabolic stresses, such as bent shock and immune response. We have isolated and sequenced a cDNA encoding ubiquitin from the silkworm, Bombyx mori. The insert in the clone is 533 nucleotide long with an open reading frame of 387 nucleotides that encodes a protein of 129 amino acids with a molecular weight of 14.8 kDa. The amino acid sequence shared high homology with the ubiquitins known so far, The result of dot blot hybridization showed that the B. mori ubiquitin gene is up-regulated upon f. rofi infection, suggesting that the B. mori ubiquitin plays an immune-related role.