In this paper we have analyzed the dualism of Raman effect with respect to wavelength division multiplexing (WDM) systems. On the one hand the impairments caused by Raman crosstalk, resulting in almost 5 dBm power difference between first and last channels, were shown. On the other, we have demonstrated that Raman effect can be used for achieving Raman amplification in optical fibers. We have come to a conclusion that in a simple case Raman amplifiers could be installed either in existing fiber optical links or in the new ones, proposing an effective amplification of 24 – channel WDM system with 50 GHz channel spacing and 10 Gbit/s bit rates. The results are obtained using simulation software, which uses an efficient time domain split step (TDSS) method for solving light propagation equation in optical fiber. Nonlinear effects, which are described in the introduction, as well as optical and electrical noises, were taken into account. The results were evaluated by means of bit error rates (BER).