Sub Macro1()
Dim i As Byte
Dim C As Range
With Sheets("Feuil1")
For Each C In .Range("a1:a" & .[A65000].End(xlUp).Row)
For i = 1 To Len(C)
x = Mid(C, i, 1)
If IsNumeric(x) Then
C.Characters(Start:=i, Length:=1).Font.Bold = False
Else
C.Characters(Start:=i, Length:=1).Font.Bold = True
End If
Next i
Next C
End With
End Sub