—This paper proposes a novel non-linear constellation mapping (NLCM) scheme for the rate compatible modulation (RCM) approach in low-to-moderate signal to noise ratios (SNRs). In NLCM, each RCM coded symbol is mapped to a complex-valued amplitude phase shift keying (APSK) constellation point. Moreover, we provide a novel method of designing code degree and weight set for a wide SNR range. The proposed NLCM is developed to increase the throughput and decrease the peak to average power ratio (PAPR) at the same time. Both analysis and simulation results show that the NLCM scheme outperforms the original RCM in terms of throughput and PAPR.