This article presents the results of the genesis investigation of Ni- and Mo-based dispersed steam cracking catalyst produced via in-situ heavy oil emulsion decomposition. The structural characteristics of catalysts and their precursors have been studied by SAXS and TEM for the first time at all stages of production and operation: in reverse emulsions, dispersions and in the coke residues obtained after catalytic steam cracking process It is shown that the Ni-based precursor is converted to larger aggregates during transition from a dispersion in heavy oil to Ni₉S₈ 10-40 nm particles in the coke residue. In the case of molybdenum this trend was not revealed, after steam cracking process two types of particles are formed: small layered MoS₂ particles with a length of 10-15 nm and larger MoO₂ 20-30 nm particles.