The structures of C5H5NiNO in a reversible photochemical reaction were studied via EXAFS, FTIR, and optical absorption spectroscopies. A photoexcited intermediate with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was generated upon irradiation using 365 nm light at 20K in a 3-methylpentane solution. The reverse reaction was induced by irradiation with 310 nm light. The EXAFS data analysis has shown a 0. 12 Å elongation of the Ni-N bond and the bending of Ni-N-O in the photoexcited intermediate. Several ZINDO calculations were conducted based on the structures obtained from the EXAFS spectroscopy. These calculations reproduced the changes in the optical spectra and the intramolecular electron transfer in C5H5NiNO.