Treatment performance and microbial community structure were investigated in water-soluble cutting oil treatment process using biological activated carbon. DOC removal in BACI column at $15^{circ}C$ was higher than at $25^{circ}C$, but those of BAC3 column after 60days was high at$25^{circ}C$. Also, quinone content of first-step reactors at $25^{circ}C$ and $15^{circ}C$ was much the same, but those of the third-step reactor at $25^{circ}C$ was higher than at $15^{circ}C$. The dominant type of two apparatus was ubquinone (UQ)-l 0 followed by UQ-8. Menaquinones were detected from $25^{circ}C$ apparatus and effluent. This suggested that DOC removal at $25^{circ}C$ was advanced degradation by attached microorganisms on the activated carbon surface. The DOC removal in long-term activated carbon apparatus increased with going in BAC3 column. This indicated the influent of POC was a result of DOC removal efficiency decrease. Integrated DOC removal from start point in experiment to break point and quinone content were showed a tendency of increasing with going last-step activated carbon apparatus. Therefore, the biological activated carbon apparatus used by this study was effective treatment process in contaminated groundwater by water-soluble cutting oil.