The free vibration characteristics of a cylindrical shell of a functionally graded three-phase composite are investigated under arbitrary boundary conditions. The novel three-phase composite is composed of graphene platelets (GPLs) in the form of functional gradient, carbon fibers with different layup angles and epoxy resin matrix. Firstly, the governing equations of motion for the cylindrical shell structure of the three-phase composite are derived based on the first-order shear deformation theory (FSDT), the Von-Karman geometric nonlinear relationship and Hamilton’s principle. Then, the natural frequencies and mode shapes of the three-phase composite cylindrical shell were discretely solved by applying the Galerkin method. Finally, the accuracy of this paper’s method is verified by comparing it with Abaqus simulation results. In addition, the effects of GPLs mass fraction, functional gradient form and boundary conditions on the intrinsic vibration characteristics of threephase composite cylindrical shells are analyzed.