An approximate method in which discrete Green functions are used is described for analyzing the free vibration of anisotropic rectangular plates with various boundary conditions. The discrete Green functions are obtained by transforming the differential equations involving Dirac's delta functions into integral equations and numerically integrating them. By employing these discrete Green functions, the differential equations governing the free vibration of anisotropic rectangular plates are transformed into the equivalent boundary integral equations, which are then solved to obtain the eigenvalues and eigenmodes. Comparisons with existing results confirm the accuracy of the numerical solutions obtained by the method. Results are presented for anisotropic rectangular plates with a number of combinations of clamped and simply supported edges and various angles of fiber orientation.