Abstract: The interfacial tension γ of cyclohexane/water interface has been determined by sessile drop method as a function of log concentration of PLURONIC copolymers(L61,L64, and F68).The influences of temperatures (10°, 20° and 35℃),etthylene oxide contents in the polymers as well as added salt (25% NaNO₃) on the γ-log C plots have been investigated. The γ-log C plots over the 0.5-1000 ppm range are convex with respect to the log C axis for all three PLURONIC copolymers used in this work.In this respect the trend is opposite to that of low molecular weight surfactants below the CMC.The reason why the Gibbs adsorption equation,at least in its usual form, may not be applied in descri-bing macromolecular solution has been discussed briefly.