Behaviors of 6 kinds of polycyclic aromatic hydrocarbons (PAH) (2, 3-dimethylnaphthalene, fluorene, pyrene, chrysene, and benzo (a) pyrene) in an activated-sludge process were studied by using a specially designed laboratory units (aeration compartment : 5l) with an Amberlite XAD-2 resin (15-20 mesh) column for adsorption of PAH in exhausted gas. One of aeration units contained activated sludge acclimated by synthetic sewage, and another unit contained only water (no MLSS) as control. One milligram of each PAH was added into both vessels. Then, the activated sludge was aerated at 1 l/min, and the water in control unit was bubbled with nitrogen gas. PAH were periodically extracted from aeration liquor and the XAD-2 column attached to laboratory units for 90 hr after addition of PAH, and extracts were analyzed by gas chromatography.The following results were obtained : (1) 2, 3-Dimethylnaphthalene, fluorene, and phenanthrene were easily volatilized and removed to the XAD-2 column by aeration.(2) Pyrene, chrysene, and benzo (a) pyrene adhered to the upper inside-wall of the vassel, and were not detected in the XAD-2 column.(3) Amounts of PAH volatilized and removed from the unit containing activated sludge were 1-10% of those from the control unit.(4) 2, 3-Dimethylnaphthalene, fluorene, phenanthrene were rapidly degraded and their degradation percentage were 87%, 95%, and 99% respectively after 90 hr.(5) Pyrene, chrysene, and benzo (a) pyrene were degraded at a slow rate and their degradation percentage were 68%, 74%, and 73% respectively after 90 hr.