The aim of this paper is to assess the biodegradation of phenanthrene by Flavobacteria FCN2 which was isolated from coke plant sludge via a classical shaken liquid medium enrichment method. The strain FCN2 can decompose phenanthrene (50 mg l(-1)) completely within 5 days. The values of pH decrease to 6.7 from 7.2 during degradation periods. And a detailed phenanthrene metabolism was assayed by using FTIR, UV and GC-MS. For FTIR, appearance of new broad absorption bands at 2858 cm(-1), 2927 cm(-1), 2955 cm(-1) and another new strong absorption band at 1734 cm(-1) in metabolites demonstrates that carboxyl group produced during phenanthrene degradation. Besides this, a very strong absorption band appears at 1260 cm(-1). It is ascribed to C-C stretching vibration band in carbonyl group of arone. Two weak adsorption at 334 nm and 349 nm in UV spectra were assigned to the n-pi* transition of CO of aldehyde. Two metabolites, phenanthrene-dihydrodiol and naphthalene-1-diol were identified in neutral fraction of phenanthrene degradation by using GC-MS. As a result carboxylic acids and arone were generated during biodegradation of phenanthrene by Flavobacteria FCN2.