CUGatesDensity is an extension of the original quantum circuit analyser CUGates (Loke and Wang, 2011)  to provide explicit support for the use of density matrices. The new package enables simulation of quantum circuits involving statistical ensemble of mixed quantum states. Such analysis is of vital importance in dealing with quantum decoherence, measurements, noise and error correction, and fault tolerant computation. Several examples involving mixed state quantum computation are presented to illustrate the use of this package. © 2013 Elsevier B.V. All rights reserved.