Thrust roller bearings are widely used in heavy-duty mechanical components, but there is a major challenge that it needs for regular inspection of the lubricants to prevent bearing failure caused by leaks, wear, and contamination from impurities. Here, we have developed a prototype of a highly sensitive self-sensing smart thrust roller bearing (SS-TRB) based on triboelectric nanogenerator for the real-time monitoring of lubricating oil. The SS-TRB consists of four thrust cylindrical rollers, a cage, a seat ring, block-shaped stainless steel electrodes, copper film electrodes, polytetrafluoroethylene (PTFE) insulation film, and lubricating oil. The open-circuit voltage (Voc) of the SS-TRB are correlated to the applied load, rotational speed, and lubricating oil content. The SS-TRB can serve as a diagnostic tool for monitoring contaminants in lubricating oil because the Voc of the SS-TRB can directly reflect the presence of stainless steel powder, carbon powder, and alcohol in the lubricating oil. Additionally, the SS-TRB exhibits the remarkable sensitivity to the water content, as even a minimal intrusion of 0.01% can trigger a significant Voc change. This work has promising prospects in demanding applications, particularly in the heavy underwater equipment.