Although concurrency control has been recognized as an important issue in XML data management, there are still few previous works that provide the concurrency of transactions retrieving and modifying the same XML documents. To overcome this problem, we propose a new XPath-based concurrency control scheme, called XPCC, that guarantees high concurrency and serializability of concurrent transactions to the same XML document. The proposed approach considers unrestricted XML documents and general XPath query, and the key ideas of XPCC are as follows: (1) semantic locks are set on XPath expressions used in transaction accesses, and (2) two versions of an XML document, a version containing updates of each transaction and a version containing updates of all concurrent transactions, are utilized for conflict checks. In XPCC, at the time that each transaction access is requested, the conflict to violate serializability is detected based on the equivalence check for results of XPath evaluation against two versions of documents. Since the proposed approach enables locking to be at the level of precise data actually retrieved and updated in XML documents, high concurrency can be achieved assuring serializability in XML data management.