Sub Sample()

    Dim lastRow As Integer
    Dim rng As Range
    lastRow = Sheets("Sheet1").Range("A65000").End(xlUp).Row

    For i = 1 To lastRow
        Set rng = Sheets("sheet2").Range("A:A").Find(Sheets("Sheet1").Cells(i, 1))
        If rng Is Nothing Then
            Sheets("Sheet1").Cells(i, 1).EntireRow.Interior.Color = vbRed
        End If
    Next
End Sub