LB films incorporating the J-aggregate of cyanine dyes, N, N'-dioctadecyl-oxacyanine perchlorate (S9) and N, N'-dioctadecyl-thiacyanine perchlorate (S11), were prepared by using octadecane as the matrix molecule. Absorption spectra of the LB films were measured in wide temperature range. It is observed that the absorption tail of S9 and S1 1 J-band depends on temperature. For the low-energy tail of the J-band, the absorption coefficient at temperatures between 6.0K and 293 K obeys the Urbach-Martienssen rule. The low-energy absorption tail of the longer wavelength peak of the S9/S11 mixed aggregate is also expressed by Urbach-Martienssen rule. A₀ and E₀ values depend on molar mixing ratio X of two dyes.