We experimentally demonstrate simultaneous 3R regeneration of 4 40-Gbit/s WDM channels, which is based on the four-wave mixing (FWM) in a single dispersion-shifted fiber. The multichannel 3R regeneration performance is validated by bit-error rate (BER) measurements. Receiver powers at a BER of are improved by 5.2 dB, 4.8 dB, 3.3 dB, and 3.9 dB for the four WDM channels, respectively. Mitigation of the interchannel nonlinearities is achieved mainly through an interchannel 0.5-bit slot time delay, which is introduced by differential group delay. Bidirectional propagation and polarization multiplexing are also applied to relieve the interchannel FWM.