The XDR technique was used for studying a series of high-loaded (90%) nickel catalysts with silica as a textural promoter. These were catalysts for direct cracking of methane at 550(degrees)C. A relation between the initial average size of active catalyst particles, carbon yield and average methane conversion was demonstrated. Genesis of these catalysts was studied including oxide precursors, reduced catalysts prior to the reaction, as well as catalysts upon their contacting the reaction medium for various periods of time from 15 min to 2 h. The active catalyst particles were shown to merge or disperse at the outset of the reaction depending on their initial size. Anyway, close average sizes ranging from 30 to 40 nm were observed by the end of the first reaction hour for all the catalytic systems providing the carbon yield of 300-385 g/g Ni. The catalytic system was shown to self-organize in the course of direct methane cracking, i.e., the catalyst particles transform in response to the reaction conditions. If the size of nickel particles cannot vary, these catalysts are inefficient for the given process.