Although several type systems have been investigated for XML, parametric polymorphism is rarely treated. This well-established typing discipline can also be useful in XML processing in particular for programs involving “parametric schemas,” i.e., schemas parameterized over other schemas (e.g., SOAP). The difficulty in treating polymorphism for XML lies in how to extend the “semantic” approach used in the mainstream (monomorphic) XML type systems. A naive extension would be “semantic” quantification over all substitutions for type variables. However, this approach reduces to an NEXPTIME-complete problem for which no practical algorithm is known, and, moreover, the type system obtained in this way is characterized by a hardly useful expressiveness. In this paper, we propose a lighter-weight way of extending the semantic approach, where we interpret type variables as markings in data values for indicating the parameterized subparts. As a result, we can construct a sensible polymorphic type system both with a semantic flavor and a set of practical algorithms needed for typechecking. Most of these algorithms can be obtained by local modifications to existing ones for a monomorphic system.