Epoxy/polyethersulfone (PES) blends were prepared without using solvent by dissolving the PES in the curing agent. Morphological structure and rheological behaviors of the blends during the reaction-induced phase separation were studied. At various PES loadings, different morphologies of the blends were obtained: sea-island structure formed with the low PES loading (10% PES), nodular structure formed with the high PES loading (30% PES), and interesting layered structure or capsule-like structure as a whole formed in the middle PES loading (20% PES) where the outer layers consisted mostly of the epoxy-rich phase. The evolution of reaction-induced phase separation process and final morphology of various Epoxy/PES blends were investigated by optical microscopy, SEM and rheometry, It was suggested that at certain PES loading, bicontinuous structure formed and grew in size at the early stage of phase separation, then the PES-rich network became shrinking, and epoxy-rich domains eventually flew out to be outer layer. Therefore, layered structure could be formed mainly based on the dynamic asymmetrical phase separation and hydrodynamic flow process. Moreover, the curing temperature conditions, such as temperature gradient in the thickness direction of the sample were also found to play a big role in the structural formation. With the addition of graphite nanoplatelet in the optimized epoxy/PES composites, an enhancement of thermal conductivity was also obtained due to the formation of thermally conductive network.