The mechanism of DON removal in the secondary effluent by ozonation and adsorption was investigated in this study. The water quality parameters, such as DON, DOC, NH4+-N, UV254 and pH etc, were determined. The variation in DON, DOC andUV254 in ozonation and adsorption tests measured, and the molecular weight distribution, hydrophilicity and hydrophobicity of the DON were then analyzed. The changes of DON in the secondary effluent were characterized using three-dimensional fluorescence spectroscopy. The results showed the removal of DON, DOC andUV254 were about 33.9%, 21.2% and 66.7%, respectively, at ozonation test and the dosage of ozone was 8mg/L. The removal of DON, DOC and UV254 were about 43.4%, 27.6% and 92.2% at the activated carbon dosage of 2.0g/L. By the combination of ozonation and adsorption the removal of DON was approximately 83.3% and 81.5%. Ozonation and acitivated carbon adsorption had opposite effects on the molecular distribution of DON. The proportions of smaller (20 000) ones were decreased by the former and increased by the later. Both treatment could increased the proportion of hydrophilic DON, and decreased them of hydrophobic and transitional DON. 3DEEM revealed that the variation of DON in ozonation and adsorption tests depended intimately on tryptophan protein-like and aromatic protein-like substances, and fulvic acid-like respectively.