1,3-Phenylenebis(5-tert-butyl-3-phenyl-2-phenyinitrene) (m-4) was generated by photolysis of the corresponding precursor diazide m-3 in 2-MTHF at 3 K with a high-pressure Xe lamp, and its ESR spectrum was measured. The observed ESR spectrum was analyzed by computer simulation based on the eigenfield / exact diagonalization hybrid method to give two sets of zfs parameters: \D\ = 0.323 cm(-1) and \E\ = 0.0 16 cm(-1) \D\ = 0.340 cm(-1) and \E\ = 0.011 cm. The temperature dependence of ESR signal intensity of m-4 in the temperature region of 3-70 K was a linear relationship in the intensity vs reciprocal temperature plot, indicating that m-4 is in a quintet ground state.