Orthogonal multiple access/multiplexing (OFDMA/OFDM) techniques represent the radio interface technologies for the next generation broadband access networks. WiMAX system adopts them for point-to-multipoint transmission. In a typical cell radius deployment of one to tree kilometers, WiMAX systems can be expected to deliver capacity of up to 40 Mbps. However the co-channel interference due to cell frequency reuse can lead to decreasing performance. In particular, throughput and BER can get worse drastically. In this paper we deal the evaluation of interference in a WiMax cellular system. Analysis is carried out. using a semi-analytical approach based on a general expression of the SINR accounting for multipath, frequency and time offsets between the reference terminal and the interfering devices. Performance have been obtained under different operating modes of the OFDMA/OFDM cellular network that is synchronous and asynchronous BSs. © 2006 ACM.