  The Characteristic Angle (CA) method [Lei Zhou and Ruibao Tao, J. Phys. A,
{\bf 27} 5599] developed previously for the easy-plane spin-1 magnetic systems
has been successfully extended to the spin-3/2 case. A compact form of the CA
spin-3/2 operator transformation is given, then the ground state energy, the
magnon dispersion relation and the spontaneous magnetization are discussed for
an easy-plane spin-3/2 ferromagnet by using the CA method. Comparisons with the
old theoretical methods are made in the end.
