In the present work, different ashless detergent/dispersant additives based on propylene oxide (PO) were prepared via reaction of propylene oxide with different tertiary amines and the products which obtained were reacted with different organic acids. The structures of the prepared compounds were confirmed using fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) for determination of molecular weight. All the prepared compounds were found to be soluble in lubricating oil. The efficiency of the prepared compounds as antioxidants and detergent/dispersant additives for lubricating oil was investigated. It was found that the additives have excellent power of dispersion, detergency and the most efficient additives as antioxidant those prepared by using n,n-dimethyloctadecylamine and di-n-butyl dithio phosphoric acid.