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In this letter, we propose a recursive channel estimation scheme for orthogonal frequency division multiplexing (OFDM) over amplify-and-forward (AF) relaying channels. Among pilot-symbol aided channel estimation techniques, linear interpolation is considered to be a simple and practical method. However, linear interpolation for the source-relay-destination channel may not work well due to the severe frequency selectivity of the cascaded channels. Specifically, extrapolation for edge subcarriers significantly distorts the channel estimation performance. To mitigate the detrimental effects of extrapolation, we partially null the channel estimates at the edge subcarriers. The proposed method effectively reduces the error propagation due to inaccurate channel estimates. In addition, we design a low complexity recursive linear interpolation scheme in which each update process utilizes both the reliability of feedback information and the characteristics of linear interpolation.