An electron spin transient nutation (ESTN) method based on FT-pulsed ESR spectroscopy was for the first time carried out for identifying the ground-state high spin multiplicities of stable pi-aryl based molecules in organic glasses. The transient nutation frequencies (omega(n)) observed from the molecules in frozen toluene were interpreted using an equation, omega(n)=omega(1) [S(S+1)-M(S)(M(S)-1)](1/2), expected for an S, M(S)-1> <-> S, M(S)> single transition in the weak microwave irradiation limit. omega(1) is a frequency that depends on the strength of an irradiated microwave pulse field. The observed nutation frequencies clearly depended on the S and M(S), identifying directly that the ground states of the molecules were triplet and quartet from the viewpoint of quantum spin nutation phenomena. The usefulness of the ESTN spectroscopy for the identification of spin multiplicity was illustrated to be a complement of cw-ESR spectroscopy.