A two-step approach for quantifying plate-like structural laminar damages, such as delamination in composites, is presented in this study. The approach first employs a 2-D continuous wavelet transform to locate the size and edges of damage from the vibrational curvature data. This is followed by an analytical inverse method to determine the flexural stiffness reduction ratio along a given direction to quantify the severity of the delamination damage. The damage quantification algorithm employed in this study is derived from the 1-D inverse method originated from one of the authors’ previous work. It is found that the two-step approach applied in beam-like structures can be extended to the damage detection of plate-like structures. A numerical example is used to demonstrate the viability of the proposed approach for the damage detection of a cantilever composite plate containing a single delamination damage. It is also found that the inverse method can provide a detailed information of delamination with a bounded searching space and can also be used to determine the effective flexural stiffness for complex delamination damage.