Monolayers composed of a xanthene dye (OFL or ORB) or a coumarin dye (HUF or HCM) and a polar matrix consisting of one or two long alkyl chain molecules (arachidic acid; C₂₀, dimethyl, dioctadecylammonium bromide; DDA, stearylamine; SA) were formed at the air-water interface and transferred onto a quartz plate by the Langmuir-Blodgett (LB) technique. Absorption and luminescence properties of dye monolayers were compared with those of CH₃OH-water solutions of the corresponding dyes without long alkyl chains (FL, RB, UF, CM). The absorption spectrum of OFL monolayer at the air-water interface considerably depended on the nature of matrix molecules and pH of the subphase. The absorption spectrum of C₂₀ OFL monolayer was composed of monomer bands of acidic and basic forms of the dye, while those of DDA: OFL and SA: OFL monolayers consisted of the basic form of the dye. A polymer band was observed in the C₂₀ DDA: OFL monolayer at high surface pressures. The fluorescence of OFL in LB films and FL in solutions was assigned to the basic form of the dyes even when they were in the acidic form. Similar results were obtained in umbelliferone (HUF, UF), but rhodamine B and aminocoumarin (ORB, RB, HCM, CM) were fairly insensitive to the nature of matrix molecules and solution pH. These findings are interpreted in terms of the acid-base equilibria of dyes which are influenced by positive (DDA, SA) and negative (C₂₀) charges of the matrix molecules, pH of the solution, as well as electronic excitation of dye molecules. Fluorescence decay and sensitizing actions of some of the dyes were briefly discussed.