To spell check a protected worksheet in Excel, first make sure that the worksheet is unprotected. To do this, go to the Review tab and click Unprotect Sheet. If you are prompted for a password, enter the password and click OK. Next, click the Spelling button on the Review tab. The Spelling dialog box appears. Select the options you want and click Check Spelling. When you're finished, protect the sheet again by going to the Review tab and clicking Protect Sheet. Enter a password if you want one and click OK.