Spin densities for nitronylnitroxide, phenyl nitronyl nitroxide(PNNO) and p-NPNN in the β-phase crystal were calculated by UHF, APUHF and UKS B(S)-LYP methods. Ab initio UHF overestimated a negative spin densitiy induced on the α-carbon atom of nitronylnitroxide group by spin polarization effect, whereas the approximately spin-projected UHF(APUHF)/6-31G* method provided a reasonable negative spin density on the α-carbon atom and almost equal distributions of the spin densities on nitrogen and oxygen atoms in PNNO and p-NPNN, in accord with the recent experiments. The spin populations on the benzene ring in these species by APUHF/6-31G* and APUHF/INDO, and UKS B-LYP/6-31G* methods were similar to the experimental values, indicating the important role of the spin polarization effect.