The toughness of structures is essential to prevent catastrophic failure. This study introduced a design framework to improve the toughness of 3D-printed carbon fiber-reinforced composite structures by local latticing utilizing the intermediate material fraction obtained in the topology optimization. The framework was based on anisotropic topology optimization considering material fraction and material orientation. The optimized results were de-homogenized by the phase field-based technique to determine the 3D printing path. Experimental validations were carried out on a three-point bending beam problem. As a result, it was shown that the framework endowed toughness for the 3D-printed carbon fiber-reinforced composite structure. (2023 Elsevier Ltd.)