Thermal stress-induced failure in the free edge region of various thin carbon/epoxy composite laminates(1mm thick) has been investigated using the three-dimensional finite-element stress analysis, ultrasonic C-scan and microscopic observations. High thermal in-plane and interlaminar stresses were predicted in the interior layer near the free edge boundaries of the laminates. In the interior lamina, not in the skin lamina, of the thin laminates with lay-up of $[0_2/90_2]_s,;[45_2/-45_0]_s,;[0_2/60_2]_s$ treated by liquid $N_2$ immersion, many transverse matrix cracks took place due to thermal stress concentration, which agreed qualitatively with the above predictions.