The peptide was extracted from fishery wastes by enzymolysis and then separated into three components by polarity with macroporous resin. The amino acid and elemental composition of three peptides were determined. Results showed that peptides contain amino acids with sulfur-based groups and N-heterocyclic groups, which was beneficial for lubricating property of peptides as additives. Furthermore, three peptides all showed excellent solubility in glycol solution (water and glycol, v
=1:1) at the concentration of 3% (mass fraction). The thermal decomposition temperature of peptides was beyond 250 ℃, indicating the good thermal stability of peptides. The tribological properties of polypeptides in water glycol solution were also studied, and the tribological mechanism was proposed. SRV test showed that peptides can significantly improve the antifriction performance of glycol solution between steel/steel friction pairs. The average friction coefficient of peptides lied between 0.135~0.144 in comparison to 0.186 of glycol solution. Three peptides are similar in anti-friction performance and the concentration of peptide in glycol solution has little influence on that. The 3D optical surface profiler was utilized to determine the volume of wear scar and results showed peptide could protect the surface of the friction pair effectively. The peptide with smallest polarity showed strongest anti-wear performance, and the wear volume was reduced by 55.49% compared with glycol solution. In load ramp test, the seizure in friction coefficient curves appear at 350, 250 and 350 N for three peptides, in comparison to 200 N for glycol solution. It was indicated that all three peptides can significantly increase extreme pressure properties of glycol solution, which might be related to the existence of sulfydryl and N-heterocyclic groups of some amino acids. It should be noted that the sulfur content of peptide is relatively low compared to other extreme pressure additives, therefore peptide can not cause serious environmental pollution and corrosion of machinery and equipment. The SEM micrographs of worn surface showed that the wear types of glycol solution were abrasive and adhesive wear, and the worn surface lubricated by different peptides was evidently smoother than that of glycol solution with shallower scratches and less stripping pits. The maximum depth of peptides was also significantly less than that of glycol solution. Moreover, XPS analysis showed the existence of carbon- and nitrogen-based organic compounds, as well as iron-containing oxides such as Fe2
, Fe(OH)O, FeOOH. The signal of sulfurated compounds was relatively weaker, due to the low content of sulfur in peptides and also the low load in tribological test. Based on the above results, the lubricating mechanism of peptide as aqueous lubricating additive was proposed. There are many polar groups in the molecular structure of the peptide, including hydroxy, carboxy and amino, which is conducive to the physical adsorption of the peptide on the metal surface. On the other hand, the peptide also forms a layer of chemical reaction film on the metal surface which is mainly composed of organic compounds containing carbon and nitrogen and iron oxides. Therefore, the excellent tribological properties of fishskin peptides result from the synergistic effect of tribological reactions and physical adsorption. This study not only provides a new idea for the efficient and rational utilization of fishery waste resources, but also lays a foundation for the research and development of new environment-friendly aqueous lubricating additives.