An operating method of a storage controller which includes a high level decoder and a low level decoder includes generating first data that is a result of decoding initial data read from a nonvolatile memory device, and a first syndrome weight indicating an error level of the first data. The first data is output to a host when the first syndrome weight is a specific value. The high level decoder having a first error correction capability is selected to decode the first data, when the first syndrome weight exceeds a reference value, and the low level decoder having a second error correction capability lower than the first error correction capability is selected to decode the first data, when the first syndrome weight is the reference value or less.