An anti-bacterial and analgesic bioactive peptide named MAS-Ⅳ-4 was isolated from the skin mucus of M. albus and purified by Sephadex G-50 gel chromatography and DEAE Sepharose Fast Flow ion exchange chromatography. The molecular weight of MAS-Ⅳ-4 was estimated by Tricine-SDS-PAGE as 10.4 kD, and its melting point was measured by microscopic melting point meter as 208~211 ℃. The anti-bacteria activity of MAS-Ⅳ-4 was assessed by determination of the inhibition zone. The results showed that the growth of Aeromonas hydropnila, Staphylococcus aureus and Bacillus subtilis was strongly inhibited by MAS-Ⅳ-4. In addition, the pain threshold of the mice was significantly increased when 0.75 ml or more of MAS-Ⅳ-4 were injected. MAS-Ⅳ-4 also demonstrated weak hemolytic activity and serine protease inhibiting activity.