Mixtures of diblock copolymers (DBCPs) and mono- or bidisperse nanorods (NRs), are systematically investigated via dissipative particle dynamics simulations. For the mixtures of DBCPs and monodisperse NRs, we investigate the effects of the nanorod (NR) volume fraction, NR length, and interaction strength between blocks and NRs on the self-assembly of the composites. For the mixtures of DBCPs and bidisperse NRs in which the NRs are different in length, the binary NRs with varied compositions can induce various morphological transitions, as well as present the uniform orientations and discriminative distributions. The inherent mechanism for driving such rich phase behaviors can be further exploited on the basis of considering the enthalpic and entropic effects. The results provide some guidelines for engineering nanocomposites with the desired morphologies and functions. (C) 2010 Elsevier Ltd. All rights reserved.