An electric fuel injection system is thought to be one of the most effective methods for improving thermal efficiency of the marine diesel engine. Nippon Kokan K. K. have developed a new type of fuel injection system, which uses a hydraulic servo-mechanism and injection control system, based on an optimal control algorithm for a higher speed engine. The performance of these systems examined on the test engine showed higher controllability and a large amount of reduction of fuel oil consumption. The control algorithm was established as being applicable to the practical system with no problems.