In this article, a novel micro/macromechanical theory is proposed for flexural analysis of 3D braided rectangular plate subjected to lateral loads. This theory is based on a novel micromechanical equivalent layerwised multi-unit cell, combined with macromechanical full layerwise theory, so called equivalent full layerwise/multi-unit cell theory (EFL/MUC). A 3D braided composite is considered as a cell system, where elastic properties of each cell depend on the position of cell in cross-section. Instead of acquiring the global elastic constants of 3D braided, three theoretical layers layers are established, and the elastic constants of each layer are acquired separately. This micromechanical procedure makes this model in agreement with macromechanical full layerwise theory. Based on this theory, the governing differential equations are derived for flexural analysis of rectangular 3D braided plate subjected to lateral loads. The problem is solved with Galerkin and finite element method. A MATLAB code is developed and the stress components in 3D braided plate subjected to lateral load, solved by EFL/MUC theory, are calculated throughout the plate only by inserting the fundamental properties of matrix, fiber and geometrical properties of a 3D braided composite system. The stress distribution in 3D braided composite plates, solved by EFL/MUC theory, seems quite different from that of isotropic plates, solved by equivalent single layer theories. The differences will be discussed in this thesis. Furthermore, after establishing equivalents and volume averaging throughout 3D braided composite the micromechanical results of EFL/MUC are compared with experimental and those of other researches in the field. Keywords: 3D braided composite plate, equivalent full layerwise/milti-unit cell theory, flexural analysis, lateral load