Fly ash is a solid residue produced during the combustion of solid fuels such as coal and biomass. Depending on the fuel type the ash content is different, but ash production in large energy plants is huge regardless of combusted fuel. In this study, two kinds of ashes (coal and biomass fly ashes) were selected for investigation taking into account the Si/Al ratio (SAR – silica alumina ratio). These ashes were characterised by high metal contents (including Al, Na, K, Ca, Mg, Fe, Ti, Ni) what is crucial in potential application as catalysts in pyrolysis process. To enhance their catalytic properties, the ashes were modified to prepare zeolites by treating with NaOH and impregnated with transition metal solution. A detail characteristic of studied ashes and zeolites was performed to determine chemical composition (X-ray fluorescence spectrometry), phase composition (X-ray diffraction), morphology and structure (scanning electron microscopy), surface area (Brunauer-Emmet-Teller method) and thermal stability (thermal analysis). Intermediate pyrolysis of agriculture biomass with ash catalyst and non-catalyst was conducted under nitrogen atmosphere at 700 C. During the pyrolysis, char, oil and gas were obtained and the yield of process was determined. The main focus was on composition and yield of pyrolytic gas proving good catalytic properties of prepared ash catalysts. After some pyrolysis cycles the usage of catalyst was investigated analysing the changes in structure and phase composition. The regeneration of catalysts was done, too. After the regeneration the studied catalysts did not change specific surface area noticeably.