Langmuir-Blodgett (LB) films incorporating two kinds of unsymmetrical merocyanine dyes (MC (X)/MC (Y) X, Y=O, S, Se) have been fabricated by using octadecane (OD) and arachidic methyl ester (AME) as the matrix molecules; MC (X);MC (Y): 0D;AME = (1- x ); x : 1: 1. Absorption spectra of the MC (X) assembies and the mixed assemblies (MC (X)/MC (Y)) have been measured in wide temperature range T =6.0-293 K. The relationship between the absorption coefficient of the low-energy tail of the aggregate band and incident photon energy has been analyzed in the framework of the Urbach-Martienssen (UM) rule. It has been found that the steepness parameter a versus T plot for each x is useful for the classification of the types of the mixed aggregate.