In forest ecosystems, forest production, storage and carbon flow are calculated based on biomass measurements. The aim of this study was to compare the biomass and carbon stock of the above-ground, litter and soil in the oak decline and control plots in Chaharmahal and Bakhtiari province. Four one-hectare sample plots were selected in the healthy (control) and declined stands of oak. Then quantitative information of all trees were measured. Allometric equations were used to calculate the above-ground biomass and carbon stock. Ten microplots were established in each sample plot and all litters were collected. Wet and dry weights and carbon content of the litter samples were measured. To measure soil organic carbon, five soil samples were taken in each sample plot. The results showed that above-ground biomass in the control and decline sample plots were 31.4 and 15.8 tons/hectare respectively. Also, the average of the above-ground carbon stock in the control and decline plots were 15.1 and 7.7 tons/hectare, respectively. The mean of litter carbon in the control plots was 1584.1 kg/ha and in the decline plots was 1148.6 kg/ha. The amount of carbon, nitrogen, phosphorus and soil moisture content showed a significant difference between the control and decline plots. The results of this study indicated significant changes in biomass, carbon stock and soil in declined stands of oak which may cause irreparable damage to the Zagros forest ecosystem, in the long term. This issue highlights the need for the attention of managers and decision makers of natural resources, regarding the provision of management solutions to control this phenomenon.