A comparison of polyacetylenes (PA) prepared with rare earth(Ln) and titanium(Ti) basedcatalyst systems in regard to the isomerization rate, conductivity and doping behaviour is presented.It is found that PA synthesized with Ln-catalyst showed the lower isomerization rate than Ti-PA.Room temperature conductivity of I2-doped Ln-PA is higher than that of Ti-PA under the sameconditions, this might related to the uniform conjugation length of Ln-PA. The difference in the doping behaviors was observed for cis and trans PA films and the complicated doping behavious of cis-PA could be attributed to the simulataneously occurring isomerization reaction during doping.