Marsh, formerly of Popstars group Hear'Say, says she faces a challenge to pull off her singing parts.
The 35-year-old, who plays Michelle Connor in the ITV soap, will portray Corrie legend Elsie Tanner (Pat Phoenix).
Speaking on This Morning, she explained: "I still do a little bit of singing here and there.
"But this is kind of completely different, and to be going and being a part of such a huge musical production is quite scary.
"Obviously I'm going to be putting in the hours and rehearsing and everything. But I'm looking forward to it."
Marsh recently told Digital Spy that she felt a "bit of pressure" about playing the role of Elsie Tanner.
> Click here to read Digital Spy's full interview with Kym Marsh
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