Monolayers containing a novel Rhodamine B dye having two long N-alkyl chains were formed at air-water interfaces and transferred to the surface of SiO₂, SnO₂, and Au substrates by the Langmuir-Blodgett (LB) technique. The single-photon counting method was used to investigate the fluorescence decay of Rhodamine B in the LB films whose absorption and emission spectra were measured by a conventional manner. The fluorescence lifetime nearly equal to the natural lifetime of Rhodamine B was observed in the LB films in which the average distance of chromophores was about 10Å. Concentration quenching of the fluorescence of Rhodamine B in the LB films was not so distinct as that reported in the adsorbed dye films by a number of research groups even at high surface dye concentration. It appears that LB films containing the novel Rhodamine B dye are particularly useful for the study of dynamics of excited dye molecules, because they are superior in many aspects homogeneity and reproducibility of dye layers, to the adsorbed dye films. Electrontransfer quenching of the fluorescence in the presence of a quencher (N, N'-dioctadecyl viologen), as well as at the surface of solid substrates capable of accepting electrons from the excited dye molecules (SnO₂, Au), was examined and the results were interpreted in terms of electronic redox levels of dye, quencher and the energy bands of the solids