Abstract: The time-temperature dependence of flexural strength of glass fiber reinforced plastics (GFRP,volume fraction of glass fiber:57%) laminates was studied by the accelerated testing method at high temperatures. The three-point bending tests were carried out at various temperatures and constant loading rates. The time-temperature dependence of GFRP laminates was investigated by means of the flexural strength master curve and time-temperature shift factor curve. The failure mechanisms at low temperature for short time to failure and at high temperature for long time to failure were investigated. With tensile delay fracture tests of the glass fiber, the time-temperature shift factors of flexural strength at various low temperatures for short time to failure were modified. The revised time-temperature shift factor curve of flexural strength of GFRP laminates agrees well with that of the dynamic Young’s modulus of the resin matrix. The flexural strength of GFRP laminates depends strongly on the viscoelasticity of the resin matrix.