Sub test()
Dim Mot As String
Dim NumCar As Long
Mot = "petit"
Range("B3") = Range("B1")
NumCar = InStr(1, Range("B3"), Mot)
' Si caractère spécial, le marquer
If NumCar <> 0 Then
Range("B3").Select
With ActiveCell.Characters(Start:=NumCar, Length:=Len(Mot)).Font
.FontStyle = "Gras"
.Underline = xlUnderlineStyleSingle
End With
End If
End Sub