For the development of a communication-assisting device for disabled users using simplified symbols, legibility of displayed information must be investigated. In this study, to assess the symbol legibility an experimental study was carried out by using measurement of the P300 component of Event Related brain Potentials. Measured amplitudes and latencies of the P300 component were analyzed. Result suggested that the number of association items from a symbol may be influence on the latency of the P300 component.