With the rapid development of modern industry, traditional lubricants often require a variety of additives to be used in conjunction with each other, which not only increases the cost but also causes a waste of resources. Therefore, the development of a lubricant additive with both a dyeing function and an antiwear and friction reduction performance can more effectively meet the industrial needs. Cerium sulfide (Ce2S3), with its excellent photostability, weather resistance, thermal stability, and nontoxicity, shows great potential as an environmentally friendly pigment. However, traditional methods for synthesizing Ce2S3 are typically hindered by high-temperature requirements and potential toxicity issues, which limits the broad application of Ce2S3 in lubricants. To overcome these limitations, this study employed a liquid-phase method under mild conditions to synthesize oleylamine-modified, wrinkle-free Ce2S3 nanosheets (OA-Ce2S3 NSs). The antiwear and friction-reducing properties of OA-Ce2S3 NSs in poly alpha-olefin-6 base oils were evaluated under various friction conditions with a four-ball tribometer. Experimental results indicate that OA-Ce2S3 NSs significantly enhance the friction-reducing and antiwear performance of lubricants by forming a physical adsorption film and an ultra thick tribochemical reaction film (with a typical thickness of 350 nm and a maximum thickness of up to 700 nm) on the friction surface. Furthermore, the study elucidates the lubrication mechanism of OA-Ce2S3 NSs and proposes their sliding mechanism on friction surfaces. This research highlights the potential of Ce2S3 nanosheets as lubricant additives and provides future directions for optimizing their synthesis and multifunctional applications, offering new insights into the field of lubrication science.