Abstract The complex microstructures of bidisperse nanoparticles/diblock copolymer mixtures in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory (SCFT) and the density functional theory (DFT). Special attention is payed to the role played by the block ratio and the interaction parameters between each component in the mixture. It is shown that the conformational entropy of the polymer chains, the block ratio of the diblock copolymer, the chemical difference between two kinds of particles and the steric packing effect of the particles play important roles in determining the morphologies of the systems. It is found that with the increase of the block ratio, the mixture undergoes a morphological transition from compound micelles to spherelike micelles. The increase of chemical difference between the two kinds of particles can promote the formation of “a jujube set in a cake”. When the selectivity of the particles is changed, another type of micelle emerges. Specifically, in the case where the particles are nonselective to the A- and B-blocks, ordered structures from the phase separation between the two types of particles emerge inside the micelles formed by the amphiphilic diblock copolymers in solutions.