In this letter, an M-ary extension to the soft information relaying (SIR) scheme is derived for distributed turbo codes (DTCs) to enable higher data rate wireless communications with extended ranges. The M-ary based SIR design for DTCs is based on constructing a revised mapping constellation of the signals for calculating metrics from the soft mapping symbols. The numerical results show that DTCs using the proposed M-ary SIR with gray mapped quadrature phase shift keying (QPSK) provides a significant 5 dB performance gain over hard information relaying (HIR) DTCs at the 10-3 bit error rate (BER) level.