SpaceWithin Property

Returns or sets the amount of space between base lines in the specified text, in points or lines. Read/write Single.

Example

This example sets line spacing to 21 points for the text in shape two on slide two in the active presentation.

With Application.ActivePresentation.Slides(2).Shapes(2)
    With .TextFrame.TextRange.ParagraphFormat
        .LineRuleWithin = False
        .SpaceWithin = 21
    End With
End With