Thiophosphate- and amino-containing polymers-poly[diethyl 2-(methacryloyloxy) ethyl phosphate-stearyl acrylate] (PPS) and poly(2-dimethylaminoethylacrylate-stearyl acrylate) (PNS)-were synthesized, and their characteristics at an oil/metal interface under a high load and rotary velocity were investigated by the measurement of the temperature of the oil, the frictional coefficient, and the electrical contact resistance between the two metal surfaces. The experimental results indicated that PNS most effectively limited the increase of the oil temperature and the frictional coefficient at low temperatures. However, PNS reduced the oil temperature and frictional coefficient less effectively than the base oil at high temperatures, whereas PPS most effectively reduced the oil temperature and frictional coefficient and increased the electrical resistance at high temperatures. Moreover, the adsorption layers of PPS could be directly observed with scanning electron microscopy (SEM). These adsorption layers were analyzed by energy-dispersible spectrometry to determine the phosphorus content and by electron spectroscopy for chemical analysis to demonstrate the existence of ferric or ferrous ions of sulfide or sulfate. The results of this study suggested that the adsorption layer of the thiophosphate-containing polymer resulted in chemisorption by a reaction of the thiophosphate group on a metal surface. In contrast, an amino-containing polymer was physically adsorbed onto a metal surface at low temperature, although no adsorption layer was observed at a high temperature with SEM.