Rate-t/k (t <= k) intercarrier interference (ICI) canceling codes for orthogonal frequency division multiplexing (OFDM) systems are proposed. The capacity lower bounds of OFDM systems employing these codes are derived for time-varying frequency-selective channels. The optimal codes maximizing these bounds are designed numerically. The simulation results indicate that the optimal codes. can provide both higher capacity lower bounds and lower bit error rates (BERs) than the existing ICI canceling codes.