In this paper, the flexural behavior was investigated at different temperatures and different cross-head speeds with and without diffusion effect. The studied material is carbon fiber reinforced derakane epoxy composite. The testing temperature was set at 30, 50, 80 and 100°C to investigate the temperature effect on flexural strength. At each temperature, the testing was conducted at four different cross head speeds (0.05, 0.2, 2 and 20mm/min). The diffusion effect was studied on flexural strength with specimens soaked in sea water at 50°C to saturate. A master curve of flexural strength was formed based on time-temperature superposition principle (TTSP) with shift factor obtained by DMA test. Based on the master curve, the flexural strength was predicted with a 35% drop after using 30 years in an ideal condition without considering pressure, stress, diffusion and so on.