Hi In order to serialize a derivative class of boost/filesystem/path, one cannot access the base class member m_path without changing its visibility from private to protected: I would suggest to change the visibility of this m_path member from private: to protected, or to add an implicit definition of the serialize method into the class boost::filesystem::path. #include <boost/filesystem/path.hpp> namespace boost { namespace serialization { class access; }} class OSD : public boost::filesystem::path { private: friend class boost::serialization::access; friend std::ostream & operator<<(std::ostream &os, const OSD&); template<class Archive> void serialize(Archive &ar, const unsigned int version) { ar & m_path; } }; Regards Francis ANDRE