When you insert a category axis title, you can click on the title, and it
will behave much like a regular text box. You can click where you want in
the text and hit Enter.
--David

Hi Extra,

The labels created by PowerPoint's graphing program (MSGraph) can not have
manual line break inserted while they are still graphs tied to a data table.
MS Graph is a fairly limited program.  I haven't played with this in VBA
code, but it may be possible to write a small macro to add these.  However,
if you ungroup the chart (and therefore unlink it from the table) than the
individual textboxes can have line returns inserted.

Hi,

If you can use vba here is a routine to replace spaces in the header row
or  column of the msgraph data sheet. If the text contains multiple
spaces you might want to pick a special character, such as ^, and insert
that in the text before running the code.

Sub x()
'
' Replace space in axis label with new line
'
    Dim lngRow As Long
    Dim lngCol As Long

    With ActiveWindow.Selection.ShapeRange.OLEFormat.Object
        With .Application
            If .PlotBy = xlRows Then
                lngCol = 2
                For lngCol = 2 To _
.Chart.SeriesCollection(1).Points.Count + 1
                    .DataSheet.Cells(1, lngCol).Value = _
                        Replace(.DataSheet.Cells(1, lngCol).Value, _
" ", vbCrLf)
                Next
            Else
                lngRow = 2
                For lngRow = 2 To _
 .Chart.SeriesCollection(1).Points.Count + 1
                    .DataSheet.Cells(lngRow, 1).Value = _
                        Replace(.DataSheet.Cells(lngRow, 1).Value, _
" ", vbCrLf)
                Next
            End If
            .Update
            .Quit
        End With
    End With

End Sub

Another possible option, depending on chart type, is to use data labels
as axis labels. You can then manually edit the data labels and add new
lines.

Cheers
Andy