Innate immunity is the most important line of defense in both vertebrates and invertebrates against pathogenic microbes such as bacteria, fungi, and viruses. Antimicrobial peptides play very important roles in the innate immune system of insects that rely solely on innate responses to combat a wide array of pathogens. Today insects are referred to as the vast resources of modern medicines. In recent years, biotechnologists and entomologists have emphasized the bioengineering of insect proteins and the applied of their products in the treatment of diseases and modern medicine. Considered drugs in this field include powerful antimicrobials against Gram-positive and Gram-negative bacteria and HIV. In this study, for the first time in the world, a novel antimicrobial peptide from an immunized lepidopteran insect, Ectomyelois ceratoniae was purified and characterized and named as Ectocin-1. The Ectocin-1 was fractionized by reversed phase high-pressure liquid chromatography (RP-HPLC). The sequence of peptides was also determined by tandem mass spectrometry. Ectocin -1 has 8 amino acid residues (LNELPGVH) with a molecular weight: 878.00 Da, Theoretical isoelectric point (pI): 5.24, Formula: C39H63N11O12, Total number of atoms: 125, the instability index (II) is computed to be 32.83, this classifies the protein as stable, Aliphatic index: 133.75, Grand average of hydropathicity (GRAVY): -0.050. The composition of amino acid residues revealed that Ectocin -1 is a hydrophobic, positively charged. Minimal growth inhibition concentration (MIC) measurements for Ectocin -1 showed antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria. Ectocin -1 did not show hemolytic activity toward human, sheep, hen red blood cells. According to the results of this study, this insect can be a good candidate for further study in complementary studies of antimicrobial activity.