Litter decomposition is a key step to the nutrient cycle and energy flow in wetlands. It is also an important process in maintaining wetland functions. Using the litter bag technique, this paper examines the decomposition rates and their influencing factors by investigating three wetland macrophytes in the Sanjiang Plain, Northeast China: Calamagrostics angustifolia, Carex meyeriana, and Carex lasiocapa. It was found that during the experiment period of 164 days, the litter of C. meyeriana had the highest decomposition rate, but the rates of the other two types of litter varied. From Days 1-103, the litter of C. lasiocapa had a higher decomposition rate than that of C. angustifolia, but this was reversed during Days 104-164. Such differences led to different weight losses after the 164 days: C. meyeriana lost 28.91 per cent of its weight, C. angustifolia lost 31.98 per cent and C. lasiocapa lost 32.99 per cent. Another finding was that the amount of organic carbon in the litter of C. angustifolia and C. lasiocapa fluctuated, but continuously decreased in that of C. meyeriana. However overall, all three types of litter released organic carbon. The N concentration fluctuated in the litter of C. angustifolia, but increased continuously in the litter of C. lasiocapa. C. meyeriana showed an increase in N concentration from Days 1-103, and a decrease during Days 103-164. N was released substantially from the litter of both C. angustifolia and C. meyeriana, but accumulated in the litter of C. lasiocapa. In contrast to the variation in N concentrations, P concentrations in all three types of litter apparently decreased first and then slightly increased. Overall, P release was observed in all three types of litter. Finally, the C/N and C/P ratios varied significantly in the decomposition process. The litter decomposition rates of C. angustifolia and C. meyeriana were strongly related to their C/P values, while the decomposition rate of C. lasiocapa correlated strongly with the P content of its litter. This paper concludes that the main environmental factors influencing the decomposition rates were soil moisture, soil bulk and soil temperature. This experiment suggests that the decomposition rates and nutrient content variations were simultaneously influenced by the quality of the litter as well as environmental factors. However, in the Sanjian Plain, they were more strongly affected by the quality of the litter.