Abstract: Decomposition characteristics such as decomposition dynamics, decomposition rate and leaf substrate quality affected by forest age were manipulated by mesh bags in 21-,29-and 36-year-old Pinus tabulaeformis stands in the middle hilly lands of Yingpan,Yanqing Country of Bejing in 2005.The results showed that the minimum discrepancy was in the decomposition dynamics,indicating that the decomposition rate exhibited rapid-slow-rapid trend in all three stands with different ages and the decomposing rate was slower during the period from May to July in 2006 than that in 2005.The decomposition rate of the leaf litter was 26.97%,26.10% and 23.96%,respectively.The half-turnover and turnover among the three stands were 2.21,2.29 and 2.54 years as well as 9.54,9.91 and 10.94 years,respectively.However,the importance of the decomposition rate,half-turnover and turnover in the forests was not significant but at 0.1 level.The N content of the leaf litter was the most affected by age(P=0.004),followed by the crude ash(P=0.028).The contents of cellulose,lignin,coarse fat and coarse protein were not significant at the 0.1 level.Although the ratios of both C/N and lignin/N in the leaf litter were affected by forest age markedly,the relation coefficients of the both ratio and decomposition rate were-0.333.