In the frequency-selective fading environments, the error probability performance of orthogonal frequency., division multiplexing (OFDM) is severely degraded by the subcarriers where the deep fading occurs. The frequency-domain adaptive bit and power loading is a very effective method to improve this situation. However, it is not always useful, e.g., in the frequency-flat fading scenarios, its performance gain over the fixed loading may shrink or even disappear. In order to deal with this issue, we propose an adaptive loading scheme which is based on the estimation of the frequency-selective fading severity. This scheme is tested based on an ultra high-data-rate OFDM system which is capable of supporting beyond 100 Mbps data rate transmission in the air interface. The numerical analysis results show that it is very necessary to employ such an adaptive loading scheme to broad-band OFDM System in the scenarios where both the frequency-selective and frequency-flat fading may be encountered.