Abstract: The effect of warp and pick densities of plain fabrics to interlaminar fracture toughness (Mode Ⅰ and Mode Ⅱ)of glass-fiber plain fabric/epoxy was studied by double cantilever beam (DCB) and end notch flexure (ENF) tests. It is found that the densities of fabric will influeuce the delamination fracture toughness evidently. The problem of interlayer matrix rivetting in woven-reinforced composite materials was proposed. Moreover,the relation between rivetting and G_IC and G_IC values was researched.