Lysozyme, the bacteriolytic enzyme, is one of the factors of the innate immunity in insects. A cDNA sequence encoding a lysozyme was isolated from the fat bodies of sweet potato hornworm, Agrius convolvuli immunized with E. coli K12 D21. The coding region of this lysozyme consists of a 19 residues signal peptide and a 120 residues mature protein, which is very similar to that of other lepidopteran. Thirteen negatively (Asp and Glu) and twenty two positively (Arg, Lys and His) charged amino acids were found in this sequence. Eight Cys residues were conserved in the same positions of other insect lysozymes.