Co-operative online bibliographic system and services (COBISS) has been developed for more than 20 years by the Slovenian Institute of Information Science (IZUM). COBISS is applied in the libraries of almost all Balkan countries and in more than 100 libraries in Serbia. There is a XML export of data from COBISS since 2002, but this segment is not studied carefully in Serbian libraries. In the same time, XML becomes more important for the librarians as the digital libraries are developing. The paper will present the XML export from COBISS as well as some possibilites for the transformations of this format using XSLT.