EPR parameters such as zero-field splittings (zfs) and anisotropic g values of rare-earth metal centered porphyrin monomers, Y(TPP)(+) and Y(OEP)(+), and double-decker dimers, [Y(TPP)(2)](-), [Y(OEP)(2)](-), and [La(TPP)(2)](-), were measured in the lowest excited triplet (T-1) states by a time-resolved electron paramagnetic resonance (TREPR) technique. The zfs parameter D of Y(OEP)(+) was smaller than that of ZnOEP, and its g(zz) was smaller than that of Y(TPP)(+). From the analyses of these data and the temperature dependence of the steady state EPR spectra, it was found that the decreases in the D and g, values of Y(OEP)(+) were due to a spinorbit coupling between the Jahn-Teller split T-1 and T-2 states. By comparing the D values of the dimers with those of the corresponding monomers, we estimated a charge resonance character, b(2), as 0.34, 0.26, and <0.25 for [Y(OEP)(2)](-), [Y(TPP)(2)](-), and [La(TPP)(2)](-), respectively. The b(2) value was larger for the OEP dimer than those for the TPP dimers. We evaluated the b(2) values using a semiempirical calculation and showed that b(2) was larger for the 3(a(1u)e(g)) electronic configuration than that for the (3)(a(2u)e(g)) configuration.