PseAAC: A flexible web server for generating various kinds of protein pseudo amino acid composition. The pseudo amino acid (PseAA) composition can represent a protein sequence in a discrete model without completely losing its sequence-order information, and hence has been widely applied for improving the prediction quality for various protein attributes. However, dealing with different problems may need different kinds of PseAA composition. Here, we present a web-server called PseAAC at, by which users can generate various kinds of PseAA composition to best fit their need.