Mode I and mode II interlaminar fracture behavior of plain glass woven fabric composites with different silane concentration was investigated on the basis of a discussion of the effects of annealing on the fracture behavior. The fracture mode changed by annealing from stable to unstable manner in lower silane concentration and from unstable to stable manner in higher silane concentration specimens in mode I fracture. In the mode II fracture, the initiation values of fracture toughness increased by annealing without respect to silane concentration.