Abstract: Organoclay/polyethersulfone(PES)-epoxy composites with different organoclay mass fractions were fabricated by solvent method and melting method. The microstructures and mechanical properties of the composites were studied. The toughening mechanisms of composites were revealed. T800H-organoclay/PES-epoxy composite prepreg unidirectional tape was prepared by adding T800H(12K) carbon fiber into organoclay/PES-epoxy composites. Composite unidirectional laminates were prepared with autoclave process. The mode I and mode II interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites were studied. Results show that the interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites and organoclay/PES-epoxy composites incorporated with organoclay mass fraction show similar trends, which supportes the proposed toughening mechanism.