In this study the large deflection behaviors of stiffened annular functionally graded (FG) sector plates under mechanical and thermo-mechanical loadings with various boundary conditions are investigated. Material properties are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Based on first-order shear deformation plate theory (FSDT) and von Karman relations for large deflection, nonlinear equilibrium equations are developed. Dynamic relaxation (DR) numerical method combined with the finite difference discretization technique is used to solve the plate nonlinear equations. Effects of material grading index, boundary condition, stiffener depth to the plate thickness ratio and thermal gradient are discussed.