Time resolved fluorescence spectra and their lifetimes of 3, 3'-diethylthiacyanine and chloride 3, 3'-diethyl-9-methylthiacarbocyanine iodide were obtained from analyses of their decay curves observed with N₂ pulse laser. It was confirmed that fluorescence of dimers decayed faster than monomers, excited singlet states of cis monomers decayed faster than its trans monomers, and their lifetimes were several nanoseconds. The decay analyses were somewhat erroneus because of very short lifetimes, Then we tried various methods to overcome the difficulty and obtain accurate decay curves.