This study focused on the initiation of a transverse crack in cross-ply CFRP laminates under fatigue loading. Transverse cracks induce more serious damages, such as delamination or fiber breakage. It is essential to understand the mechanism of the transverse crack onset under fatigue loading for improving long-term durability and reliability of CFRP laminates. Therefore, a method to evaluate and predict the initiation of a transverse crack in cross-ply CFRP laminates under fatigue loading was proposed. Fatigue tests at various stress levels were performed to evaluate the initiation and multiplication of the transverse cracks. Fatigue tests were interrupted at arbitrary loading cycles to observe damage in cross-ply CFRP laminates. The transverse cracks caused in the laminates were observed by an optical microscope and soft X-ray photography. The fatigue limit of transverse crack initiation in this fatigue conditions was indicated by calculating the stress applied in 90° layer of the laminates at the saturated state of the transverse cracks with a variational approach. Moreover, the analytical method on the basis of Paris law in order to predict the number of cycles to transverse crack initiation under fatigue loading was proposed. As the results, the predicted number of cycles to transverse crack initiation shows good agreement with experimental results.