Abstract: Three types of carbon-fibre epoxy composites , HT7/ 5228 , HT3/ N Y9200G and HT3/ 5224 , were interlayer toughened with thermoplastic particles. In order to improve compression st rength af ter impacting (CAI) andevaluate damage resistance , a quasi-static indentation (QSI) test was conducted. The experimental result s indicatethat the interlayer zones formed by particles and epoxy can significantly suppress delamination and crack propagation. Average delamination onset energy e_Ⅱc is significantly improved. The relation between indent depth and contactforce shows that the interleaved specimen achieves a smaller damage area at the expense of greater indent depth inthe local region. The toughening mechanism is chiefly as follows : geomet rical effect of interlayers , crack path kinking and deflection , and crack tip shielding. A large amount of f racture energy is absorbed by ductile deformationand ultimate failure of the particles.