Mesoscopic properties of water-insoluble tetrakis(4-methoxyphenyl)porphyrin J-aggregate in thin film have been investigated by time-resolved scanning near-field optical microscopy. The film was found to be composed of planar microcrystallines with lengths of a few micrometers, widths of similar to100 nm, and similar to20 nm heights. The transmittance spectra are site-specific. This observation might reflect inhomogeneity of the sample, and is related to the broad J-bands compared to those of tetrakis(4-sulfonatophenyl)porphyrin. Excited-state lifetimes, obtained from pump-probe measurements in small domains, were ranging from 10 to 50 ps that are of the same order with the far-field results. (C) 2003 Elsevier B.V. All rights reserved.