An all-optical non return-to-zero (NRZ) to return-to-zero (RZ) modulation format converter using single semiconductor optical amplifier (SOA) and an optical band-pass filter (OBPF) was proposed. By adopting the ultra-fast SOA model associated with optical system software, the 10 Gbit/s NRZ-to-RZ format conversion was successfully demonstrated with simulation. The proof-of-the-principle experiment at 10 Gbps was also demonstrated using the test SOA and OBF converter. The result shows that the BER is 1.0×10－9 when the power of RZ is －15 dBm,which are well coincidence with simulated results.