The incorporation of nanoparticles into polymer matrices increases reinforcement and leads to stronger plastics. However, controlling the spatial distribution of nanoparticles within polymer matrices is a challenge in improving the properties of polymer nanocomposite. Dissipative particle dynamics simulations are employed to investigate the self-assembly of nanoparticles into a variety of anisotropic superstructures. The shape of nanoparticle varies from hexagonal nanoplatelet to nanorod by changing the aspect ratio (S). A hexagonal particle with S approximate to 1 is spherelike. Depending on the grafted chain length and number of grafted chains, the self-assembled structure in the morphology diagram may be spherical aggregate, fillet, ribbon, or string, in addition to dispersed phase. In general, nanoplatelets tend to form string structure while nanorods have a tendency to pack as fillet or ribbon structure. The length of matrix polymer (L(m)) changes the phase boundary separating different regions in the morphology diagram. As L(m) is increased, the nanoparticle solvophobicity declines and thus results in smaller aggregates generally. Nonetheless, for weakly solvophilic grafted nanoplatelets, the string size grows with L(m) due to depletion attraction.