This letter discusses channel quantization problem in multiuser orthogonal frequency division multiplexing (OFDM) systems based on maximum subchannel signal-to-noise ratio (Max-SNR) resource allocation (RA). It is assumed that subcarriers are assigned to users according to Max-SNR RA. Then, a probabilistic quantization scheme is derived to obtain the higher rate-sum capacity via equal power approximation for water-filling. Simulation results show the proposed scheme achieves a great performance gain compared to equal distance quantization in both high-SNR and low-SNR cases. However, if 5% capacity loss is allowed, two additional feedback bits are required for the low-SNR instance due to the larger approximation error.