The FSA submarine optical amplifier system (submarine fiber using optical amplifiers) has been developed. It can transmit signals up to 10 Gbit/s with a repeater spacing of 100 km. The submarine repeaters contain optical amplifiers for six line pairs to yield a maximum capacity of 60 Gbit/s. This paper describes its system configuration, the repeater configuration, and the fiber dispersion management scheme used to realize bit-rate flexible transmission and in-service monitoring.In long-haul optical amplifier systems, since the amplified spontaneous emission noise from the optical amplifier is the main impairment limiting the transmission distance, an S N R design technique that takes this noise into account is developed. Finally, the results obtained after the commercial installation of this system in the Kagoshima-Okinawa route (total length 905 km) are reported, including chromatic dispersion characteristics and S N R values at both 2.5 Gbit/s and 10 Cbit/s transmission. The effectiveness of the system design is verified through the demonstration of good transmission performance and the feasibility of in-service monitoring.