The reductase unit of p-hydroxyphenylacetate hydroxylase contains flavin mononucleotide (FMN) as a cofactor. Fluorescence decay curves measured by fluorescence up-conversion method were remarkably dependent on monitored emission wavelength. The fluorescence lifetime was shorter at the shorter emission wavelengths and longer at the longer wavelengths. Spectral shift correlation function of p-coumaric acid in water and FMN in C-1 protein in buffer solution were expressed by two-exponential functions. Correlation times, phi(1) and phi(2), of p-coumaric acid were 0.053 and 0.650 ps, respectively, which was similar to previous works. phi(1) and phi(2) of C-1 were 0.455 and 250 ps, respectively. The Stokes shift from t = 0 to t = infinity was 2200 cm(-1), while it is 500 cm(-1) in the static Stokes shift obtained by the solvent effect of the fluorescence spectrum under static excitation. This suggests that the isoalloxazine ring of FMN in C-1 is exposed in hydrophilic environment. Such large Stokes shift was unusual among flavoproteins. The biphasic decay of the spectral correlation function in C-1 was discussed and compared to the biphasic decay of tryptophan in proteins.