We propose and demonstrate simultaneous optoelectronic NRZ-to-RZ regenerative format conversion for multiple DWDM channels using a single phase modulator (PM) and a fibre delay-interferometer (DI). In order to accommodate multiple DWDM channels, the DI is designed to have a free spectral range (FSR) equal to the channel spacing. This thus extracts the chirp induced by the phase modulation for all the channels at the same time. Since the original carriers are suppressed to some extent, the NRZ-to-RZ conversions can be achieved with regeneration. Multi-channel format conversion is successfully demonstrated for 16 channels at 10 Gb/s and 8 channels at 20 Gb/s, with a channel spacing of 100 GHz. Bit error ratio (BER) measurements at 10 Gb/s show 3.5 and 4.2 dB penalty improvements for 50 and 75 km transmission without dispersion compensation, respectively. Significant extinction ratio (ER) improvement and timing jitter reduction is observed for the converted channels.