Based on a general representation of displacement variation through the thickness of laminated plates, a Karman type nonlinear theory of laminated composite plates with weakened interfacial bonding is developed. Each weakly bonded interface is modelled by a spring-layer model which has recently been used efficiently in the field of micromechanics of composites. This springlayer model allows for a discontinuous distribution of displacements, but requires the tractions to be continuous across each interface of adjacent layers. The set of governing equations has variable coefficients in the most general form of bonding and includes conventional third-order zigzag nonlinear theory of Karman type for laminated composite plates as a special case when extreme values of interface parameters are used. Some simple numerical examples allowing for a closedform solution are presented to give an understanding of how a small amount of interfacial weakness affects the overall and local behaviour of laminated composite plates. These include the important practical problem of reduced interface stresses due to weakened interfacial bonding, which can be predicted by the theory presented herein.