Abstract: Five types of natural flake graphite (NG) with particle sizes of 10, 20, 30, 40 and 50 μm were used to prepare polyimide (PI)/NG composites via a hotpressing technology, and the dynamic thermomechanical properties, tribological performance and morphologies of fracture and worn surfaces were investigated. The results indicated that the storage modulus and loss modulus of PI were enhanced with the addition of NG, and however, they were seldom affected by the particle size of NG. Moreover, the coefficient of friction and wear rate of PI/NG composites continuously decreased with a decrease in particle size. The PI/NG composites achieved a coefficient of friction of 0.0882 and a wear rate of 6.19×10-7mm3/N·m when NG with a particle size of 10 μm was added. In addition, the PI/NG composites exhibited a smoother worn surface than pure PI, in which a more continuous and compact transfer film was obtained.