The saccade-related electroencephalogram (saccadic EEG) has researched to achieve a brain computer interface (BCI) based on intention to eye movement. The spike signal before eye movements has been confirmed as the characteristic of saccadic EEG. However, the detection ratio of spike signal is not enough to achieve the BCI. In this paper, we focus on a slow cortical potential before a saccadic eye movement. Results show the possibility that the slow cortical potential is related to the bereitschaftspotential (BP) of saccadic eye movement.