Wenn Spalte A gleicher Wert Spalte B in Zeilen...

Option Explicit
Sub jekt()
Dim i As Integer, letzteZeileA As Integer, a As Integer, n As Integer, Text As String
With Worksheets("Tabelle1")
letzteZeileA = .Cells(Rows.Count, 1).End(xlUp).Row
a = 0
For i = 2 To letzteZeileA
If .Cells(i, 1).Value = .Cells(i + 1, 1).Value Then
Text = Text & .Cells(i, 2).Value
a = a + 1
Else
Text = Text & .Cells(i, 2).Value
For n = 0 To a
.Cells(i - n, 3).Value = Text
Next n
a = 0
n = 0
Text = ""
End If
Next i
End With
End Sub