In this study, the effect of time selectivity and pilot symbol period on the performance of an OFDM system with block type based channel estimator was investigated. Performance degradation due to pilot symbol usage was determined in terms of bit error rate (BER);the pilot symbol period that gave the lowest BER was defined as the optimum pilot symbol period (OPSP). The OPSPs were calculated for seven different time selective fading channels then the relationship between these values and channels' coherence time was investigated. Results show that, OPSP can be expressed best with coherence time at 0.9 correlation (T C,0.9) and seventeen pilot symbol per T C,0.9 can be used. Using such a relationship, OPSP can be set easily by a single variable channel parameter for time selective fading channels. © 2012 IEEE.