Two novel antibacterial peptides were isolated and characterized from the earthworm Eisenia fetida. The antibacterial peptides were purified to homogeneity by means of cation-exchange chromatography and reverse FPLC and named F-1 and F-2. By means of ESI-MS, F-I and F-2 were determined to be two peptides with the relative molecular mass of 535.27 and 519.27. By means of MS/MS, the amino acid sequence of F-1 and F-2 were determined to be Ac-Ala-Met-Val-Ser-Ser and Ac-Ala-Met-Val-Gly-Thr respectively. F-1 and F-2 exibited an antibacterial activity not only to bacteria but also to fungi. Minimal inhibitory concentration (MIC) of F-1 and F-2 against several Gram-positive and Gram-negative bacteria were determined by incubating approximately 10(4)similar to10(5) CFU/ml of cell with serial dilutions of peptide in a 96-well microtiler plate. The MIC of F-1 and F-2 against Enterococcus gallinarum, Pseudomonas pyocyanea, Acinetobacter baumanii, Klebsiella terrigena 1 were 11.4 mg/L and 12.85 mg/L. The MIC of F-1 and F-2 against Enterococcus faecalis was 22.8 mg/L and 25.68 mg/L.