As the link distance or the data rate increase intersymbol interference (ISI) caused by chromatic dispersion increases and ISI mitigation becomes an important issue. The demand for reducing cost per gigabytes is one of the main reasons for using electronic equalizers which are very cost-effective. The common and useful optimization criterion to estimate the DFE coefficients is the minimum mean square error (MMSE). However, the MMSE solution does not achieve optimal performances, and the minimum BER (MBER) is the ultimate performances criterion. Here, we derive an analytical expression for the probability of error with DFE and examine the optimal optimization criterion, MBER for DFE in optical communication system. A BER performance comparison analysis shows that the MBER optimization criterion introduces improvements over the conventional minimum MSE optimization criterion.