It was shown that high-spin d(6) ions at trigonal prism and linear two coordinate sites have uniaxial magnetic properties by calculating their low-lying eigenstates under the influence of crystal field and spin-orbit coupling and then determining their g-factors for the parallel and perpendicular directions. On the basis of our theoretical findings, we interpreted the uniaxial magnetic properties of Ca3CO2O6 with high-spin Co3+ (d(6)) ions at the trigonal prism sites and those of Fe[C(SiMe3)(3)](2) with high-spin Fe2+ (d(6)) ions at linear two-coordinate sites, and discussed why compounds with high-spin d(6) ions at octahedral sites cannot have uniaxial magnetic properties.