In order to develop environment-friendly lubricant additives, ricinoleic acid and diethanolamine were used as raw materials to prepare ricinoleic acid diethanolamide (RA) by two-step synthesis method, and then ricinoleic acid diethanolamide borate (RAB) was synthesized with boric acid. The structures of RA and RAB were characterized by FTIR, and the tribological properties of RAB were investigated by using rapeseed oil as base oil. The optimal conditions for the synthesis of RA were obtained by single factor experiment: the molar ratio of ricinoleic acid to diethanolamine in the acylation reaction was 1.0:0.8, and the reaction time was 6 h at 150 ℃. The molar ratio of ricinoleic acid to diethanolamine was 1.0:0.4, the amount of sodium hydroxide was 1% of the total mass of ricinoleic acid and diethanolamine, and the yield of RA reached 88.10% at 95 ℃ for 3 h. The optimum synthesis conditions of RAB were as follows: the molar ratio of RA to boric acid was 1.8:1.0, the amount of p-toluenesulfonic acid was 1.5% of the total mass of RA and boric acid, and the yield of RAB reached 92.78% at 140 ℃ for 100 min. The rapeseed oil added with RAB formed a composite lubricating protective film containing B and N on the friction surface. When the amount of RAB was 2% of the total mass of rapeseed oil, the maximum non-seizure load (PB) of the oil sample increased by 61% compared with that of rapeseed oil. When RAB content was 1%, the oil sample showed good friction protection performance.