We describe here the cDNA sequence and mRNA expression of a novel serine pretense from the firefly, Pyrocoelia rufa. The 771 bp cDNA encodes for 257 amino acid residues. The deduced protein of P. rufa serine pretense gene contains the catalytic triad and six-conserved cysteine residues. Alignment of the deduced protein of P. rufa serine pretense gene showed 47.4% protein sequence identity to known coleopteran insect Rhyzopertha dominica midgut trpsin-like enzyme. Northern blot analysis revealed that the P. rufa serine pretense is specifically expressed in the midgut of P. rufa larvae.