This work evaluated an amperometric biosensor based on multi-wall carbon nanotubes (MWCNT), chemically modified with methylene blue (Met) and horseradish peroxidase (HRP), for detection of phenolic compounds. The dependences of the biosensor response due to the enzyme immobilization procedure, HRP amounts, pH and working potential were investigated. The amperometric response for catechol using the proposed biosensor showed a very wide linear response range (1 to 150 μmol L-1), good sensitivity (50 nA cm-2 μmol -1 L), excellent operational stability (after 300 determinations the response remained at 97%) and very good storage stability (lifetime > 3 months). Based on all these characteristics, it is possible to affirm that the material is promising for phenol detection due to its good electrochemical response and enzyme stabilization. The biosensor response for various phenolic compounds was investigated. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.