五氯酚是生物制菌劑並廣為木材加工業者所使用，而污染到土壤及地下水，以生物復育方式可處理土壤之五氯酚污染，復育成效則視降解菌之多寡而定，本研究利用自台灣南部的某廢棄木材加工場場址收集受污染土壤，分離五氯酚降解菌，以低成本且較為簡易的最大可能數法(most probable number)進行五氯酚降解菌菌數之估算，利用五氯酚降解時產酸使培養基pH值下降值與五氯酚殘餘濃度作為菌種生長之判斷指標並與含五氯酚之平板計數(plate count)法相較，結果顯示結果顯示當培養基pH值下降0.4個單位時即可判斷為五氯酚降解菌生長之正反應，且此二測定法之測定結果具有極高之相關性 Pentachlorophenol (PCP) is a biocide used around the world as a wood preservative, its widespread use has led to contamination of soil and groundwater. The success or failure of bioremediation depends on the presence or survival of PCP-degraders in the environment. In the study, the PCP-degraders were isolated from contaminated soils from a wood-preserving industrial site. The mineral salt medium containing PCP plate count and new most probable number (MPN) method for determination of PCP-degraders using the pH-drop. Even though the pH drop indicating PCP degradation was very small (<0.4), it could show the result obtained from the PCP concentration analysis. There was a high relationship between the results of all MPN counts and plate counts.