The magnetic properties of N-[(dichlorophenyl)thio]-2,4,6-tris(chlorophenyl)phenylaminyl radical crystals are reported. The stable radical crystals of N-[(2,4-dichlorophenyl)thio]-2,4,6-tris(4-chlorophenyl) phenylaminyl (1) and N-[(2,4-dichlorophenyl)thio]-2,4,6-tris(3-chlorophenyl) phenylaminyl (2) have shown one-dimensional ferromagnetic behavior which have described using the Bonner-Fisher model with the large ferromagnetic exchange interaction of J/k(B) = 14.0 K and J/k(B) = 5.7 K, respectively. In addition to these ferromagnetic compounds, N-[(3,5-dichlorophenyl)thio]-2,4,6-tris(4-chlorophenyl) phenylaminyl (3) has also shown the ferromagnetic intermolecular exchange interaction of J/k(B) = 1.8 K. For these crystals, we have carried out low-temperature susceptibility and heat capacity measurements below 2 K. Radical 1 has shown a magnetic phase transition at 0.4 K. The suscepttibility in the ordered state, however, shows spin-flip transition, indicating antiferromagnetic long range ordering.. For the ordered state, the interchain interactions are also estimated to be J’/k(B) = 0.02 K and J " k(B) = 0.01 K. In order to clarify electronic structures, ab-initio molecular orbital calculations of their substituted radicals are carried out. The correlation between the magnetic interactions and the electronic structures is discussed.