Axis.ScaleType (Word)

Returns or sets the value axis scale type. Possible return values are xlScaleLinear - A linear scale, xlScaleLogarithmic - A logarithmic scale.

With ActiveDocument.InlineShapes(1) 
 If .HasChart Then 
 .Chart.Axes(xlValue).ScaleType = xlScaleLogarithmic 
 End If 
End With