Abstract: The film pressure vs. area curves of the surface films of three PLURONIC polyoxyethylene-polypropylene polyols (with molecular weight in the range 2×10~3- 8×10~3) , three all heteric polyoxyethylene-polypropylene polyols (with molecular weight in the range 1.5×10~6-2.5×10~6), and two polypropylene glycols (with mo- lecular weight of 2025 and 2×10~6) have been determined on a saturated sodium nitrate (46%) aqueous solution substrate. Based on the analysis of experimental data, it is proposed that the polyoxyethylene-polyoxypropylene polyols molecule orients at the air/water interface with the EO chain partialy lies in the interface and partially immerses in the water phase. The fraction of the number of EO unit lain in the interface in creases progressively with film pressure, but independent of n_(EO), the ethylene oxide chain length. The same is ture for propylene oxide (PO) chain, except the fraction of the number of PO unit lain in the interface is much smaller than that of the number of EO unit lain in the interface at the same film pressure. With this model and the assumption that the fractions of the number of EO and PO units lain in the interface are independent each other, the surface film data of PLURONIC polyols and all heteric polyoxyethylene-polyoxypropylene polyols can be related with the results of polypropylene glycols and TRITON type surfactants quantitatively. Based on the experimental data of the surface films of three all heteric polyoxyethylene-polyoxypropylene polyols on a pure water surface, it is suggested that in this case the EO chain of the molecule not only is easily soluble in water, but also trends to tring part of PO chain to penetrate the water phase.