Abstract <p>The shape of filler particles and features of the interaction between the polymer and the filler can play an important role in the structure formation of polymer nanocomposites. At present, nanoparticles (NPs) of natural aluminosilicates, graphene, MXene, and layered double hydroxides are considered as promising fillers. These NPs can form diverse spatial ordering types within self-assembling polymer matrices. In this work, we analyze the NP effect on the microphase separation in the polymer matrix using the mesoscale computer model of a nanocomposite based on an asymmetric AB diblock copolymer filled with 2D NPs. All computations are performed within dissipative particle dynamics. The results show that at a certain composition of the copolymer (A₇B₁₃), the introduction of NPs into a polymer matrix initiates a transition of the gyroid morphology (GYR) formed by A and B blocks to the lamellar one (LAM) through the formation of an intermediate metastable structure such as perforated lamellas (PL). The GYR-PL-LAM transition is detected in the strong incompatibility mode of copolymer blocks and A blocks with NPs and good compatibility between NPs and B blocks. The observed effect is interesting because of the possible application of 2D NPs in the design of nanocomposites with controlled behavior.</p>