This paper is evaluating the addition of nanocobalt on dry matter, organic matter, cel-lulose and hemicellulose degradability of In-vitro gases technique. Nanocobalt as an addi-tive were used as 0, 25, 50, 75, 100 and 125% from the animal requirements on DM basis. The regular ration (1:1 concentrate: clover hay) was incubated for 24 hours. Then 24 and 48 hours of dry matter, organic matter, cellu-lose and hemicellulose were used to research the impact of adding 25 and 50% nanocobalt to some roughages (rice, bean, wheat, bagasse and peanut) straws using In-vitro disappear-ance. Results of In-vitro gas indicated that the DMD degradability values were increased (P<0.05) in 50 and 75 %, while the highest of OMD was in 25 and 50 % of nanocobalt. The nanocobalt had no effect on pH, but had a greater influence on the values of ammonia and TVF's, as well as the degradability of cell wall components with microbial proteins. In control ration, the gas production was high, adding cobalt (100 %) and nanocobalt (25 and 50 %) than other of addition. High values of microbial protein (MP) and microbial protein efficiency (EMP) recorded for all different nanocobalt added. Nanocobalt 25% output gas of DM, NDF, ADF, cellulose and hemicellu-lose showed increase (P<0.05) compared to any additional levels. It concluded that the ad-dition of nanocobalt increased the production of gas, ammonia, TVF's, metabolizable energy and degradability of cell wall constituents. It showed that the addition of nanocobalt had a stronger effect on disappearance of all roughages as DM, OM, NDF, ADF, cellulose and hemicellulose. Furthermore, the addition of 25% nanocobalt had a significant effect (P<0.05) on improving In-vitro DM and OM disappearance of all roughages except bagasse had a significant effect in add 50 % nanoco-balt.