Abstract: For the last 10 to 27 years, artificial forests had been located in rehabilitated lands in the upper reaches of the Yellow River.The objective of present study was to compare the carbon densities of various layers under artificial and natural forests.Following are the results of the comparison.Under artificial plantations, the vegetation layer (including roots) has a mean carbon density of 111.3 t/hm², the litter layer has a density of 5.1 t/hm² and soil layer contains 164.9 t/hm².These values account for 28.6 %, 13.8 % and 61.0 % of their respective counterparts in the natural secondary forests under the same site conditions of the area.The ratios of carbon density among vegetation, litter and soil layers are 39.6:1.8:58.6 for artificial forests and 57.4:2.7:39.9 for natural forests.As well, the carbon densities of the vegetation and litter layers are increasing exponentially with forest age.Also, their total carbon density ratios are increasing gradually.Although the mean total carbon density of the present artificial forests in the rehabilitated lands is 281.2 t/hm² in the experimental area, it accounts for only 41.5 % of the carbon density of the natural secondary forests (677.4 t/hm²).In the artificial forests, the annual increase in total carbon density is as high as 15.2 (t/(hm²·a), which is 11.7 % more than that of the natural forests and 6.8 times higher than the corresponding value (1.95 t/(hm²·a) of artificial forests in the entire country as measured for the years 1994 to 1998.This indicates better growth and carbon storage capacity of artificial forests in the rehabilitated lands compared with that of the barren hills and the secondary forests.It can be concluded that the scientific pursuit and continuing conversion project from cropland to forest and grass land is very important in the formation of carbon sinks and reduction of the greenhouse effect.