The suspended substance (SS) in the effluent from eco-biofilters was examined by elemental analysis and infrared spectroscopy. The inorganic components of SS in D1 and S1 are more than those in D2 and S2, respectively. The IR spectra of SS is mainly composed of the adsorption of carbohydrates, protein, etc. The domninating bands near 1655, 1542 and 1240 cm(-1) are assigned to amide I, amide II and amide III respectively, and the characteristic IR absorption of protein could be one of the significant components of cell walls. The peak near 1460 cm(-1) is attributable to the bending stretching of CH1-- and CH3--. The strength of adsorption peaks in the region 1720-1200 cm(-1) for D1 is lower than that for D2, but at 1040 cm(-1) the case is reversed.