We have investigated the E.P.R. spectra of Gd 3 + in KY 3 F 1 0 single crystal. Gd 3 + substitutes for Y 3 + in an eight-fold fluorine coordinated site forming an antiprism (GdF 8 ) 5 - . We have determined the fine structure and transferred hyperfine structure spin hamiltonian parameters. The former are discussed by using the superposition model of Newman and we compare our values with previous ones obtained for Gd 3 + center in other host crystals as in LiYF 4 and ReF 3 (Re = La, Ce, Pr, Nd) which allows us to propose intrinsic parameters for eightfold fluorine coordinated Gd 3 + . The latter indicate some spin polarisation effect of the Gd 3 + 5s and 5p shells due to inner unpaired 4f 7 electrons.