We obtained a biosurfactant from filtrate (BS) of activated sludge acclimatized to tetrachloroethylene (PCE)．Solubility of PCE by addition of the filtrate increased approximately 2.5 times compared with that by water. In this case, the peaks of particle size distribution of filtrate changed from 64 and 248 nm to 389 and 4,053 nm, indicating that PCE was emulsified by BS. The emulsifying activity of the PCE filtrate was highest among tested Tween 20 and Sodium Surfactin (SF)．Abilities of oil-film surface area exclusion ratio using raw petroleum of BS, Tween 20, and SF were 0.22, 0.21 and 0.15, respectively. The methanol extracted fraction of the filtrate has higher ability of oil-film area exclusion. Its spot on the Thin Layer Chromatogram showed active Ninhydrin and a maximum adsorption of UV 220 nm. These results suggested that the biosurfactant in the filtrate has peptide bonds in its chemical structure.

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