Abstract: Decomposition of fine root of the primitive Pinus koraiensis and broadleaved forests as well as its secondary Betula platyphylla and Populus davidiana forests was studied from May to October 2002 to examine the decomposition dynamic and nitrogen mineralization using litter bags.The experiments involved three forest sites during different forest succession of the primitive Korean pine and broadleaved forests,80 years and 20 years old secondary Betula platyphylla and Populus davidiana forests,respectively.In the three sample plots,the decomposition speed was fast at initial stage,and then it was slowing down gradually.In the primitive forests,the fastest decomposition rate of fine root was Fraxinus mandshurica,followed by Pinus koraiensis,and the slowest one was Tilia amurensis.In two secondary forests,fine root decomposition rate of P.davidiana was faster than that of Betula platyphylla.The fine root decomposition was affected not only by the chemical properties of tree species but also by stand environment.In the three plots,N would release or concentrate during the fine root decomposition.In spring and autumn,N would release because of the lower air temperature and the less rainfall.In summer,N would concentrate because of the higher air temperature and more rainfall.