Objectives of this research are mainly to study impacts of acidity strength (by varying amount of precipitant and loadingAl-Si) and the effect of nickel particle size (by varying calcinations temperature) on decomposition reactionperformances. In this research, high-nickel-loaded catalyst is prepared with two methods. Ni-Cu/Al catalysts wereprepared with co-precipitation method. While the Ni-Cu/Al-Si catalyst were prepared by combined co-precipitation andsol-gel method. The direct cracking of methane was performed in 8mm quartz fixed bed reactor at atmospheric pressureand 500-700°C. The main results showed that the Al content of catalyst increases with the increasing amount ofprecipitant. The activity of catalyst increases with the increasing of catalyst's acidity to the best possible point, and thenincreasing of acidity will reduce the activity of catalyst. Ni-Cu/4Al and Ni-Cu/11Al deactivated in a very short timehence produced fewer amount of nanocarbon, while Ni-Cu/15Al was active in a very long period. The most effectivecatalyst is Ni-Cu/22Al, which produced the biggest amount of nanocarbon (4.15 g C/g catalyst). Ni catalyst diameterhas significant effect on reaction performances mainly methane conversion and product yield. A small Ni crystal sizegave a high methane conversion, a fast deactivation and a low carbon yield. Large Ni particle diameter yielded a slowdecomposition and low methane conversion. The highest methane conversion was produced by catalyst diameter of 4nm and maximum yield of carbon of 4.08 g C/ g catalyst was achieved by 15.5 nm diameter of Ni catalyst.