In wireless orthogonal frequency division multiplexing (OFDM) systems in order to reduce channel impairments, and increase system performance channel estimation must be implemented. This paper investigates; the impact on channel estimation mean squared error (MSE) performance of pilot density and placement for the channels that have different time variant transfer function. The time and frequency intervals between the pilots that give the lowest MSE determined as the optimum pilot intervals. Then these intervals are related to channels' coherence time and bandwidth at 0,9 correlation respectively. It is seen from the results that by using approximately 2, 8 pilot symbols per B c, 0.9, and 2, 6 pilot symbols per Tc, 0.9 the optimum pilot interval can be calculated easily. Therefore with the use of this relationship the optimum pilot placement is determined with reduced computational complexity. © 2013 Croatian Society Electronics in Marine - ELMAR.