Molecular J-aggregate formation in Langmuir-Blodgett (LB) films and polymer films has been investigated. Mixed monolayers 5,6,5’,6’-dibenzo-1,1’- diethyl-2,2’-cyanine chloride (Sh), 1-methyl-1’-octadecyl-2,2’-cyanine perchlorate (S120) with arachidic acid (AA) (Y-type) and 1,1’-diethyl-2,2’-cyanine iodide (PIG) and Sh in sodium alginate (SA) films were deposited onto quarts. substrates. The LB films and the polymer films were built-up with different dye concentrations. By means of the time-correlated single-photon counting technique, the fluorescence lifetime of the J-aggregates of cyanine dyes has been measured. The evidence of the excitation energy transfer from the donor J-aggregate (S120 or PIG) to the acceptor J-aggregate (Sh) have been obtained from the fluorescence spectroscopy and the fluorescence lifetime measurements. The difference of energy transfer in the LB films and the polymer films would reflect different distributions of dyes in the each films.