The amphiphilic association structures in the system water-phenethyl alcohol and two triblock copolymers (L101: EO4.5PO59EO4.5and F108: EO132.5PO50EO132.5) (EO=ethylene oxide, PO=propylene oxide) were investigated by optical observation, measurements of surface tension, quasi-elastic light scattering and electric conductance. The results showed a most drastic influence of small amounts of the long polar chain block copolymer on the phase regions in the system water-phenethyl alcohol - (EO)5(PO)56(EO)5with 0.1% of the long polar chain compound added to the short chain one giving a most pronounced change in the phase regions.