The decomposition of plant litter is an important mechanism in regard to energy and nutrient dynamics of ecosystems. The decomposition dynamics of three plant parts of Phragmites australis (leaves, stalks and rhizomes) and the changes of total nitrogen and phosphorous concentrations were examined in Lake Balaton and Kis-Balaton Wetland for 230 days. The commonly applied litter bag technique was used, with two mesh sizes (litter bag mesh sizes ø = 3 mm; and plankton net bag mesh sizes ø = 900 μm). Leaf litter mass loss generally did not differ between the two mesh sizes and the study sites. The highest decomposition rates were observed at rhizomes (k=0.0051) and the slowest at stalks (k=0.0004). At the end of the investigation period, the remaining nutrient concentration was different in the three plant parts of P. australis. Nitrogen and phosphorous at the stalks in Lake Balaton was higher compared to the initial concentration. In the case of the leaves and rhizomes a decrease was observed.