Concentration of greenhouse gasses in atmosphere is one of the most challenging issues for human being in this century. CO2 is the main part of greenhouse gasses. In order to mitigate atmospheric CO2 and to create balance in greenhouse gasses, atmospheric carbon must be absorbed and sequestrated in organic forms. Rangeland ecosystems have approximately half of the worlds land area and they withhold over one third of terrestrial biosphere carbon. Consequently, these lands are capable of considerable carbon sequestration. Mountainous landforms in central Zagros are mainly used as rangeland. These rangelands have been degraded due to overgrazing. There is no detailed information about the effects of improper practices on carbon sequestration of these ecosystems. The objective of this study was to assess effects of different levels of degradation on carbon sequestration by sites of semi-arid rangelands in central Zagros mountain range. The rangeland sites of Fereydan- Isfahan were selected as study area. Three sites including moderate to good and degraded rangeland as well as old rainfed land were selected. The samplings method was random –systematic in 40 plot of 1 square meter along 100 m of 12 transects. In this study, the crown cover of each plot was estimated then above ground biomass, below ground biomass and litter of each plot were measured by clipping and weighting. Above-ground biomass was sampled in quadrates (50 cm × 50 cm) at each sampling site. Litter was removed from plots by hand-raking and root biomass was measured by collecting soil cores (12.5×25 cm 2 ) from depth of 0-30 cm in each plot which was co-located with the above ground biomass measurement. The below-ground samples from each segment were washed using 2-mm and 0.5 mm sieves. The soil sampled depths were 0–15, 15–30 cm. Forty eight samples were collected in each site. After traorting of soil and plant samples to lab, organic carbon of plant and soil samples were determined by burning method and Walky-Blak dichromate oxidation procedure. Then, total weight of sequestrated carbon per hectare was calculated. Data were tested for normal distribution. Analysis of DCA (Detrended Corresponden Analysis), variance, Pearson's correlation and multiple regression analysis were used to evaluate effects of sites conditions on carbon sequestration. Results indicated that the soil organic C at 0-30cm depth and total plant components between moderate to good rangeland (69.25 and 6.9 ton/ha) and degraded rangeland sites (62.62 and 6.4 ton/ha) was not significantly different. but organic C content of soil and total plant components between old rainfed land (50.3 and 2.2 ton/ha) with moderate to good rangeland and degraded rangeland showed significant difference. Results also indicated that conversion of rangelands to rainfed lands had greater effect on decrasing carbon sequestration compared to grazing pressure. Differences in plant community composition was the major factore causing differences in carbon sequestration. Generally, in this study, the soil component had the highest content (92%) of total sequestrated carbon and while biomass and litter contained 6.2 and 1.7 percent respectively. Total sequestrated carbon of belowground biomass was higher than above ground parts of plants. Keywords : carbon sequestration, rangeland,degradation levels, old rainfed land, plant community composition.