FBG (Fiber Bragg Grating) sensors were embedded into CFRP unidirectional composite laminates in a direction perpendicular to the carbon fiber. Residual strains after curing were evaluated by the reflection spectrum from the FBGs. The CFRP laminates were kept at 100 °C for monitoring of the residual strain change measured by the FBGs. Without mechanical loading, occurrence of physical aging was confirmed by the residual strain changes. The relationship between the influence of physical aging on residual strain and the thickness of the CFRP was almost linear.