Я использую этот код:
Public Shared Function Transform(xml As String, xsl As String, argsList As XsltArgumentList) As String
Dim selectedXml As XDocument = XDocument.Parse(xml)
Dim xmlTransform As New XslCompiledTransform()
Dim htmlOutput As New StringBuilder()
Dim writer As XmlWriter = XmlWriter.Create(htmlOutput)
xmlTransform.Load(New XmlTextReader(New StringReader(xsl)))
xmlTransform.Transform(selectedXml.CreateReader(), argsList, writer)
Return htmlOutput.ToString()
End Function