1,3,5-Benzenetriyltris(N-tert-butyl nitroxide (3), its 2-methoxy derivative (4), and 1,3,5-tris{ip-(N-oxy-N-tert-butylamino)phenyl}benzene (5) were prepared and studied by EPR and magnetic susceptibility/magnetization measurements. Trinitroxides 3 and 4 showed EPR fine structures characteristic of quartet states : 3 : g = 2.0062, D/hc = 0.009 32 cm-1 and E/hc = 0.000 15 cm-1; 4 : g = 2.0063, D/hc = 0.009 66 cm-1 and E/hc = 0.000 32 cm-1. The changes in the signal intensity vs reciprocal temperature obeyed Curie’s law in the range 10-100 K, suggesting that the quartets are their ground states. Magnetization data for 3 and 4 at 1.8, 3.0, and 4.0 K in the field range 0-7 T obeyed the Brillouin function in which S = 3/2. The effective magnetic moment of a crystalline sample of 4 obtained on a SQUID susceptometer was 3.21 mu(B) at 240 K, increased gradually, reached a maximum (mu(eff)/mu(B) = 3.73) at 32 K, and decreased steeply as the temperature was decreased. The results were interpreted in terms of an isosceles-triangular exchange interaction among the three nitroxide radicals within a molecule (J1/k(B) = 68.4 and J2/k(B) = 5.0 K) and antiferromagnetic intermolecular interaction (theta = -1.7 K). A methoxy group on the m-phenylene ring was found to weaken the through-ring exchange coupling among the attached nitroxide radicals by an order of magnitude. An X-ray structure analysis of a clear red block cubic single crystal of 5, Pa3BAR (No. 205), a = 18.786(2) angstrom, V = 6631(2) angstrom3, Z = 8, D(calc) = 1.301 g cm-3, revealed the molecular structure with three nitroxide groups 37.5-degrees out of the peripheral p-phenylene rings which am tilted out of the central benzenetriyl unit by 19.5-degrees in a propeller conformation. Temperature dependences of the mu(eff) values observed for crystalline and matrix-isolated 5 in the range 5-300 K gave J/k(B) values of +6.8 K (theta = -2.1 K) and +5.3 K, respectively, when analyzed in terms of a regular-triangular exchange coupling model. Lower spin polarization on the 1,3,5-triphenylbenzene chromophore is concluded to be responsible for the reduced J value in 5.