An analysis of the relationship between the EPR trigonal-field parameters and the local crystal structure of octahedral Mn2+ centre in diamagnetic garnets is presented by diagonalizing the complete energy matrices for a d(5) configuration ion in a trigonal ligand-field. Both the second-order and fourth-order EPR parameters D and (a-F) are taken simultaneously into the structural investigation. It is shown that the local lattice structure around an octahedrally coordinated Mn2+ centre in diamagnetic garnets have expansion distortions, which may be attributed to the fact that the radius of Mn2+ ion is larger than that of Al3+ or Ga3+ ion, and the Mn2+ ion will push the oxygen ligands outwards. The local lattice structure parameters R and theta for octahedral Mn2+ ion centre in the crystals are determined, respectively. Meanwhile, it is also demonstrated that the empirical impurity-ligand distance R approximate to R-H + 1/2 (r(i) - r(h)) is not suitable for Mn2+ in diamagnetic garnets, which has been approximately taken in previous works. (c) 2006 Elsevier B.V. All rights reserved.