TextFrame.HorizontalAlignment (Excel)

Returns or sets an XlHAlign value that represents the horizontal alignment for the specified object. Possible return values are xlHAlignCenter - Center, xlHAlignCenterAcrossSelection - Center across selection, xlHAlignDistributed - Distribute, xlHAlignFill - Fill, xlHAlignGeneral - Align according to data type, xlHAlignJustify - Justify, xlHAlignLeft - Left, xlHAlignRight - Right.

Some of these constants may not be available to you, depending on the language support (U.S. English, for example) that you've selected or installed.

Dim tfe As TextFrame: Set tfe = 
tfe.HorizontalAlignment = xlHAlignCenter