This paper describes the pyrolytic reaction of polyacetylene (PA) prepared with titanium and lanthanide elements based catalyst systems before and after thermo-iso-merization by PGC. A parameter suitable to compare difference in molecular structure of PA's has been suggested and applied to study. Under the given pyrolytic conditions

cis- and trans-PA showed quite similar pyrogram. A smallr change in h1/h5 ratio has been found for Ln-PA than that for Ti-PA with the increase of aging time. These results demonstrates that Ln-PA has better agnig property than Ti-PA.