Physico-chemical characteristics of raw stems of giant reed (Arundo donax L.) and of the char obtained by pyrolysis at 500 degrees C and 800 degrees C under flowing N-2, as well as char yield, were determined to examine features evolution and potential applications. The chars derived at both temperatures were found potentially suitable as solid bio-fuels. Char features and yield at the lower temperature were compared to those from pyrolysis of the stems pre-treated with a phosphoric acid solution under otherwise identical conditions. The acid treatment induced an enhanced char yield and a highly developed porous structure with surface properties similar to those characterizing activated carbons. Thermogravimetric analysis also showed substantial changes in pyrolytic behavior of the treated stems. They seem to be due to the catalytic action of the acid promoting degradation at lower temperatures compared to pyrolysis of the untreated stems.