The thermal decomposition of low-density polyethylene (LDPE) and polyvinyl alcohol (PVA) in a nitrogen flow at a temperature range of 573-873 K was investigated in the presence of Fe-containing catalyst;s. In this temperature range decomposition of these polymers with formation of gaseous (C-1-C-4), liquid (C-5-C-30), and solid (carbon, arbide, graphite) products is observed. During this process, a-FeO(OH) used as a precursor of the catalyst is reduced to iron oxides and metal, and, therefore, it is in unsteady state. The unsteady state of catalyst allows one to affect on all stages of polymer decomposition. Gas chromatography-mass spectroscopy (GCMS) and X-ray diffractometry (XRD) show that the presence of the Fe-containing catalyst greatly affect both liquid and solid products of thermal decomposition of LDPE and PVA.