Resonant ultrasound spectroscopy (RUS) was optimistically selected to study feasibility and implementation details of the testing method, in order to accomplish reliable and quick evaluation of the lattice components additively manufactured. A series of lattice structures of Ti-6Al-4V which contains planar defects of different widths was manufactured by additive manufacturing process. Experiments were carried out based on a home-made RUS system, and longitudinal ultrasonic transducers were used as the transmitter and receiver. The resonant frequencies and vibration modes were identified by setting suitable experimental parameters, and then a reliable combination of resonant frequencies was chosen to evaluate the defects by constructing a Mahalanobis space. Finally, the Mahalanobis distance was calculated for each specimen and defects were analyzed quantitatively. Experimental results show that resonant frequency peaks can be detected obviously and repeatedly even for the lattice components with complex structures. Results show that there is a strong correlation between positions of certain resonant frequency peak and the size of defect. Comparing with traditional non-destruction testing (NDT) method, RUS provides a favorable NDT solution for the lattice structure additively manufactured.