Abstract Frequency Domain Equalization for Single Carrier transmission (SC-FDE) attracted much attention due to its low complexity and performance in suppressing ISI. But SC-FDE usually can not provide soft information for Soft-In Soft-Out (SISO) decoders which Shannon limit codes relies on to achieve outstanding BER performance. In order to combine SISO decoders with SC-FDE, a method to calculate the soft information of SC-FDE output symbols is proposed in this paper, and its validity is confirmed by simulations.