In this thesis we propose two algorithms for timing synchronization in orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithms deal with low signal-to-noise ratio (SNR) and multipath fading channel with high delay spread, two factors that degrade the performance of a timing synchronizer. One algorithm is for frame synchronization, based on a well-known algorithm, Schmidt & Cox``s . By reallocating the power of transmitted signals and using a larger received window, proposed algorithm works well in low and moderate SNR with little degradation in bit error rate (BER) performance. The other algorithm derives from the observation that the synchronization in multipath fading channel can be improved when the channel is known. From that idea, we propose a symbol timing algorithm combining channel estimation and timing synchronization. One more block is added to the conventional timing synchronizer to correct the timing offset. The simulations with indoor fading channels show that the proposed algorithms outperform the previous ones.