Monolayers of the amphiphilic benzo-15-crown-5 styryl dye were prepared. Their ionoselective and photosensitive properties in the presence of K+ or Na+ cations in the aqueous subphases were investigated. The reversible changes of the reflection intensity (due to trans-cis-trans isomerization of the C=C bound in dye molecule) can be observed only for complexes of the dye molecules in monolayers with cations from the aqueous subphase.