The buckling of an orthotropic rectangular laminate with weak interfaces is investigated. The state-space formulations established directly from the 3D theory of elasticity are employed. The weak interfaces are treated in a unified way by adopting a linear spring-layer model. The present analysis is very effective because the final scale of solving equations always keeps the same in spite of the number of layers as well as the number of weak interfaces in the laminate. The solution is also completely exact that can be used as a benchmark for clarifying various plate theories or numerical methods. (c) 2006 Elsevier Ltd. All rights reserved.