Abstract: Based on the displacement and potential fields with six degrees of freedom, the equations of motion for piezoelectric composite laminates were established. The closed solutions for cross-ply rectangular piezoelectric composite laminates with simply-supported boundaries are obtained. The present theory is an equivalent single layer theory and contains only six displacement and electric variables, the number of which is independent of the layers. The equations of motion can be solved simply. The displacement and electric potential fields are depicted by the displacement and electric potential distribution functions through thickness, respectively. The three functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and electrostatics charge equation by enforcing interfacial continuity conditions and force and electric conditions at the top and bottom surfaces. The high accuracy of this equivalent single layer theory is demonstrated in the numerical examples.