In this study, the fractal behavior of crack development in damaged concrete materials and its application to structural damage assessment are experimentally investigated. The experimental results demonstrate that the crack evolving is closely related to the characteristics of fractal behavior, and the surface-crack distribution of the damaged concrete structures possesses fractal characteristics. It thus indicates that the fractal may be capable of performing quantitative characterization of crack development, which cannot be comprehended by Euclidian geometry. The application of fractal characteristics of surface-crack distribution in structural damage assessment is then investigated. By correlating the fractal dimension of surface-crack distribution with the model parameters (e.g., natural frequency) of different magnitudes of damage, a linear relationship exists between the fractal dimension and natural frequency. Since the natural frequency is one of the most fundamental damage characteristic factors, the above linear relationship shows that the fractal dimension of surface-crack distribution is able to effectively act as an effective damage characteristic factor. Different from the conventional damage characteristic factors generated from vibration tests, this factor reflects structural damage from a new perspective of fractal analysis, and provides a viable and novel approach for health monitoring and safety evaluation for concrete structures.