A new technology is adopted to improve atomic oxygen resistance characteristics of spacecraft resin matrix composites, which is to fill superfine particles into the resin matrix. The superfine plerospheres, which are non-reactive with atomic oxygen, are filled into the phenolic matrix in order to produce the AO-resistant fibre/phenolic resin composite in the paper. Plerospheres/fiber/phenolic resin composites were prepared and the AO exposure test was conducted in a ground-based AO effects simulation facility. It was found that the filling of plerospheres effectively protected the fibre/phenolic resin against AO erosion. After the AO exposure test of 50–60h, the erosion yield of the glass fibre/phenolic resin and the carbon fibre/phenolic resin with plerosphere fillers could decrease to 9% and 13% of the composite without fillers, respectively. Furthermore, the erosion yield of all the composites decreased with the increase of the filler amount.