ChartFont.Underline (Word)

Returns or sets the type of underline applied to the font. Can be one of the XlUnderlineStyle constants. Read/write Variant. Possible return values are xlUnderlineStyleDouble - Double thick underline, xlUnderlineStyleDoubleAccounting - Two thin underlines placed close together, xlUnderlineStyleNone - No underline, xlUnderlineStyleSingle - Single underline, xlUnderlineStyleSingleAccounting - Not supported.

With ActiveDocument.InlineShapes(1) 
 If .HasChart Then 
 .Chart.ChartTitle.Font.Underline = xlUnderlineStyleSingle 
 End If 
End With