The transient analysis of delaminated composite and smart composite plates is studied using a newly developed improved layerwise laminate theory, extended to include large deformation. The theory is capable of capturing interlaminar shear stresses that are critical to delamination. The presence of multiple, discrete delaminations is modeled through the use of Heaviside step functions. Stress free boundary conditions are enforced at all free surfaces and continuity in displacement field and transverse shear stresses are enforced at each ply level. In modeling piezoelectric composite plates, a coupled piezoelectricmechanical formulation is used in the development of the constitutive equations. Numerical analysis is conducted to investigate the effect of nonlinearity in the transient vibration, attributable to large displacements and rotations and bimodular behavior caused by the contact impact of delaminated interfaces. Composite plates with delamination, subject to external loads and voltage history from surface bonded sensors, are investigated and the results are compared with corresponding linear transient history, experimental results and plates without delamination.