In electronic digital signal processing based optical communication systems, digital equalization for chromatic dispersion interacts with local oscillator phase noise to produce equalization-enhanced phase noise (EEPN). In addition to both phase and intensity noises, EEPN also induces timing jitter to the equalized signal. For a 100 Gbit/s quadrature-phase-shift keying signal with laser linewidth of 300 kHz, the timing jitter is up to 20% of the symbol interval for a transmission distance of 1500 km.