Companies need various ways to compete with other companies. One way to reduce losses, regarding the number of reject products. If the reject product has reached the consumers' hands, and is not resolved immediately, the company will lose its customers. The FMEA (Failure Effect and Method Analysis) method is used to analyze the main problems that exist in the company with the RPN sorting method, so that the Reject product of the boss rotor 05K machining process can be reduced by making improvements. FMEA is done by determining the severity, incidence rate, and detection value to determine RPN. The FMEA method is used for analysis during the boss rotor manufacturing process. The manufacture of boss rotor consists of several processes, one of which is the CNC machining process and the OP30 machining which are most commonly found reject products. The data is calculated using the pareto diagram to find problematic processes. The process with the most problems will be processed with FMEA. The main problem that must be resolved on the boss rotor 05K machining is the diameter under 33 with RPN (Risk Priority Number) is 294, then the proposed improvement is to periodically maintain the machine. Daily machine maintenance such as checking the amount / size of coolant, monthly machine maintenance such as cleaning chucks and jaws and annual engine maintenance such as checking chuck cylinders for excess movement due to cylinder wear (run out). Based on these proposals, it will produce better boss rotor products in the future.