Option Explicit
Sub Comparer()
Dim DerLigne As Long
Dim Cel As Range, C As Range
Dim firstAddress As String
With Worksheets("Feuil1")
DerLigne = .Range("B" & .Rows.Count).End(xlUp).Row
For Each Cel In .Range("B2:B" & DerLigne)
Set C = Worksheets("Feuil2").Range("B:B").Find(Cel, LookIn:=xlValues)
If Not C Is Nothing Then
If C.Offset(0, 2).Value <> Cel.Offset(0, 2).Value Then C.Font.Bold = True
End If
Next Cel
End With
End Sub