With the growing popularity of XML there is a need not only to describe the structure of XML data but also its se-mantics. For the conceptual modelling of XML we can use existing conceptual models. However, special features of XML require extensions of these models. In this paper, we study conceptual modelling of XML keys. We extend the no-tion of E-R keys to be suitable for modelling the semantics of XML keys and we show how to express them on the XML logical level. 1