This paper proposes the theoretical derivation method of both the frequency spectrum and the bit error rate (BER) performance for uplink Orthogonal Frequency Division Multiple Access (OFDMA) in the presence of the nonlinear distortion. Since OFDMA has two different subcarrier allocation methods such as localized FDMA (LFDMA) and interleaved FDMA (IFDMA), there is the difference, in terms of the influence of the nonlinear distortion at each mobile station (MS) on the out-band radiation and the BER degradation, between LFDMA and IFDMA. Therefore, it is meaningful to clarify this difference by means of the theoretical approach. The feature of the proposed approach is to represent both the frequency spectrum and the BER performance by the simple series form formula, which enables us to overview these performances without any time-consuming computer simulations. The validity of the proposed formula is confirmed by the agreement with the computer simulation results with the parameters of the number of MSs and the input back-off (IBO).