An analytical method for observing the interaction between a metal oxide surface and diol compounds such as poly(ethylene glycol) and poly(propylene glycol) has been newly developed using infrared absorption and contact-angle measurements. The infrared absorbances of both poly(ethylene glycol) and poly(propylene glycol) at 3496 cm(-1) were proportional to the oil film thicknesses, but the absorbance intercepts in the plots of absorbance versus film thicknesses were negative at zero film thickness. The negative intercepts indicate that the hydroxy groups of poly(ethylene glycol) or poly(propylene glycol) disappeared owing to the adsorption of the diol compound molecules on the metal oxide surface. The contact angles of poly(ethylene glycol) and poly(propylene glycol) at 40 degrees C decreased with an increase in the heat-treatment temperature of the metal plate, but the contact angle of hydrophobic poly(propylene glycol) was smaller than that of hydrophilic poly(ethylene glycol) on the metal oxide surface. The difference in contact angle resulted from the fact that adjacent poly(ethylene glycol) or poly(propylene glycol) molecules inside the drop were connected by hydrogen bonding with the OH groups on both ends of the molecules.