Most fishing vessels in Indonesia use diesel engines as their driving force. Diesel engines are mechanical machines where component contact is unavoidable, so a lubricating system is absolutely necessary to reduce the level of component damage that intersects. The decrease lubricating system capability has an impact on engine damage. The purpose of this study is to identify the causes of damage to the diesel engine lubricating system for fishing vessels, making it easier to make decisions in carrying out maintenance and repairing lubricant systems. The method for identifying each possible failure occurs using a Preliminary Hazard Analysis (PHA) and Fault Tree Analysis (FTA). PHA is a device to identify potential hazards that result in system failure, FTA is a device to identify the causes of system failure. FTA works by determining failures which are referred to as "top events", then the top event identifies the relationship of the factors causing various failure events with fault trees that use simple logic gates "and" and "or". The formation of an FTA can determine the factors causing failure with a minimum cut set. Based on the results of the analysis, there are three main causes of diesel engines failing because the lubricating system is the failure of lubricating system components namely internal leakage (screen lubricant + pressure alarm + manometer + officer), and (lubricating pump + pressure alarm + manometer + officer).