An amperometric biosensor for the determination of phenols is proposed using a crude extract of sweet potato(Ipomoea batatas (L.) Lam.)as an enzymatic source ofpolyphenol oxidase(PPO;tyrosinase; catechol oxidase; EC 1.14.18.1). The biosensor is constructed by the immobilization of sweet potato crude extract with glutaraldehyde and bovine serum albumin onto an oxygen membrane. This biosensor provides a linear response for catechol, pyrogallol, phenol and p-cresol in the concentration ranges of 2.0×10−5-4.3×10−4mol L−1, 2.0×10−5-4.3×10−4mol L−1, 2.0×10−5-4.5×10−4mol L−1and 2.0×10−5-4.5×10−4mol L−1, respectively. The response time was about 3–5 min for the useful response range, and the lifetime of this electrode was excellent for fifteen days (over 220 determinations for each enzymatic membrane). Application of this biosensor for the determination of phenols in industrial wastewaters is presented.