Abstract: By onsite forest litter survey and buried decomposition bags, investigation and study were conducted on the seasonal litter amount dynamics and decomposing processes of forest litter in different environments in cold temperate mixed forests of riparian zones upstream Wenyu River in motane area. The annual litter production of motane riparian forests to the riparian zone and the river were 3.46 and 4.09 t·hm-2·a-1 respectively. Of the litter in both environments, the litter from broadleaves was dominant, accounting for 40.55% and 40.19% respectively, while the leaves from conifer and broadleaves accounted for 62.00% and 59.64% of total litter respectively and the branches and leaves accounted for 81.09% and 77.92% respectively. In the composition of litter, the highest litter amount was from broad leaves, then from needle leaves, branches, miscellany, flowers and fruits, barks and herbs subsequently. The annual litter dynamic curves of both environments had two peaks, with the highest amounts occurred from mid-September to mid-October, accounting for 73.46% and 76.92% of annual litter amounts respectively, and from April to June, accounting for 23.3% and 30.3% of annual amounts respectively. In the study area, the decomposition rate of leaf litter in waterbody was lower than those in subtropical forests, but higher than that in many temperate forests. The decomposition rate of leaf litter in waterbody, which was 0.712 9 with a half life of 0.97a, was faster than that in humus layer under riparian forests. Under riparian forests where are close to river banks, the decomposition rates on sun slopes were faster than that on shade slopes, while the decomposition rate and a half life were 0.531 9 and 1.30a for sun slopes and 0.433 7 and 1.60a for shade ones. At where far to river banks, the decomposition rates on sun slopes were slower than that on shade slopes, while the decomposition rate and a half life were 0.604 2 and 1.15a for shade slopes and 0.440 1 and 1.58a for sun ones.