A new theory for the non-axisymmetric elastic large de¯ection analysis of sector plates stiened by a single eccentric rectangular cross-section radial stiener is presented. In the theoretical model the reaction of the stiener on the plate is modelled partly by means of body forces in the plate equilibrium equations and by local modi®cation to the loading adjacent to the stiener. The reaction of the plate on the stiener is modelled as a distributed force system applied along the length of the stiener. The force interaction is complemented with a set of plate-stiener displacement compatibility equations. The governing stiened plate equations are then transformed into initial value format and discretised with respect to four uniform, interlacing ®nite-dierence meshes. The discrete system of equations is solved using the DR (Dynamic Relaxation) algorithm. The validity and accuracy of the new plate theory is established by comparing large de¯ection analysis results for a uniformly loaded clamped stiened sector plate with corresponding results obtained with the ANSYS ®nite element software. The career analysis is then used to conduct three large de¯ection parameter studies of simply supported and clamped sector plates stiened by a single eccentric radial stiener. Numerical results are presented to show the eect on de¯ections, stress resultants and stress couples of stiener depth, plate thickness ratio and sector angle.