The effects of the macrostructure on the solid particle erosion properties of glass-fiber composites were investigated. The erosion experimental apparatus used was an air-blast type system. The composite target was a fully aligned glass-fiber-reinforced epoxy. The erosion rates were obtained by changing the impact angle of the erodent particle beam and the orientation of the glass-fiber in the composite target as a primary experimental variable. Surface morphology of eroded samples was investigated by optical and scanning electron microscopy, both at steady-state erosion and single-impact events. Based on these activities, the essential data for the erosion processes and mechanisms were provided. The experimental data shows that the solid particle erosion of the composite is fully dependent on the fiber orientation, with the maximum and relative minimum erosion rates varying in magnitude and at different angles of impact with the changing fiber orientation in the composite. A mechanism for the erosion of glass-fiber-reinforced epoxy composite is proposed based on the macrostructural geometrical constraints imposed by the fiber-matrix system.