Experiments were designed and conducted to isolate and characterize the full length cDNA of cecropin gene from the cotton leafworm, Spodoptera littoralis. In addition, sequence and phylogenetic analyses of this gene were studied. Using differential display technique, a typical cationic insect cecropin gene (SpliCec) was isolated from bacterial-challenged S. littoralis haemolymph. Five differentially displayed bands were sequenced. Based on sequence analyses of the data, specific primers for the full length of cecropin were designed and successfully amplified 388 bp amplicon. The integration of the results revealed that the 388 bp-PCR product has one open reading frame (orf) of 186 bp long, including both start codon (AUG) and stop codon (UGA). The deduced amino acid sequence of SpliCec indicated that the full length prepropeptide consists of a 22-residue signal peptide, a dipeptide prosequence and a 38-residue mature peptide. The SpliCec sequence created significant similarity with many insect cecropin sequences, especially those of M. sexta and A. convolvuli.