Abstract: Local lattice structure distortion studies of the octahedral Mn2+ center in M(ClO4)(2) center dot 6H(2)O: Mn2+ (M = Cd, Hg) systems have been performed systematically based on the diagonalization of the complete energy matrices of electron-electron repulsion, spin-orbit coupling and trigonal ligandfield interaction for a d(5) configuration ion in a trigonal ligand field. From the EPR calculation, the local structure distortion parameters R and theta are determined, respectively. Results show that the local lattice structure around a trigonal Mn2+ center has a compressed distortion along the crystalline C-3 axis. The compression distortion may be ascribed to the fact that the radius of the Mn2+ ion is smaller than that of the Hg2+ ion and the Cd2+ ion. The local lattice structure parameters for Mn2+ in M(ClO4)(2) center dot 6H(2)O:Mn2+ (M = Cd, Hg) systems are determined at liquid-nitrogen temperature and room temperature.