In this paper, we develop a generalized Fourier series expansion theory for solving biharmonic equation in a sector-shaped domain. Using the corner eigenfunction satisfying appropriate homogeneous boundary conditions on radial boundaries, we explicitly determine Fourier coefficients appearing in the eigenfunction expansion of circular boundary data from the biorthogonality relation. The covergence of generalized Fourier series solution is shown by using the asymptotic formula for eigenvalues. Biorthogonality method derived in this paper is applied to the deflection problem of sector-shaped plate with uniformly distributed weight.
