Cost-sensitive learning has been applied to resolve the multi-class imbalance problem in Internet traffic classification and it has achieved considerable results.But the classification performance on the minority classes with a few bytes is still unhopeful because the existing research only focuses on the classes with a large amount of bytes.Therefore,the class-dependent misclassification cost is studied.Firstly,the flow rate based cost matrix(FCM) is investigated.Secondly,a new cost matrix named weighted cost matrix(WCM) is proposed,which calculates a reasonable weight for each cost of FCM by regarding the data imbalance degree and classification accuracy of each class.It is able to further improve the classification performance on the difficult minority class(the class with more flows but worse classification accuracy).Experimental results on twelve real traffic datasets show that FCM and WCM obtain more than 92% flow g-mean and 80% byte g-mean on average;on the test set collected one year later,WCM outperforms FCM in terms of stability. Cost-sensitive learning has been applied to resolve the multi-class imbalance problem in Internet traffic classification and it has achievedible results.But the classification performance on the minority classes with a few bytes is still unhopeful because the existing research only focuses on the classes with a large amount of bytes.Therefore, the class-dependent misclassification cost is studied. Firstly, the flow rate based cost matrix (FCM) is investigated. Secondarily, a new cost matrix named weighted cost matrix (WCM) is proposed, which calculates a reasonable weight for each cost of FCM by regarding the data imbalance degree and classification accuracy of each class. It is able to further improve the classification performance on the difficult minority class (the class with more flows but worse classification accuracy). twelve real traffic datasets show that FCM and WCM obtain more than 92% flow g-mean and 80% byte g-mean on average; on the test set collected on e year later, WCM outperforms FCM in terms of stability.