Abstract: Classification of chemicals by ecological hazard was studied with the multi-class support vector machines(M-SVMs)to improve accuracy and efficiency of the classification.A total of 61 environmental priority pollutants that had already been collected were analyzed for correlation between 7 inexes in the aspects of environmental behavior and biotoxicity.On such a basis a M-SVMs classification model was established and 10-fold cross validation of its dataset was conducted to evaluate classification ability of the model.Then the model was applied to predict ecological hazard of 7 chemicals.Results show that the index of daphnia toxicity,overlapping some of the information of the index of fish toxicity,was excluded from the 7 indexes.So only 6,i.e. as fish toxicity,alga toxicity,biodegradability,bioconcentration,distributivity and adsorbability were selected in building the M-SVMs classification model.The M-SVMs model was quite high in identification rate and cross-validation indicated theat its mean classification accuracy reached up to 86.89%,and its prediction of the 7 chemicals in ecological hazard basically tallies with the actual situation.