Electron Spin Eesonance (ESR) of polyacetylene (PA) prepared with rare-earth coodination catalysts have been studied. The ESB spectra of PA are found to be singlet and Lorentz. No significant changes of PA ESB by catalyst systems composed of naphthenates of all fifteen rare earth elements are observed. It was found that the ESB linewidth

Ig N (N is the unpaired electrons concentration) exhibits a straight line with the cis content

with g=2.0028±0.0001. The formation of the unpiared electrons obeys the zero-order kinetics with the activation energy 11.3kcal/mol. The lightly I2 doped rare-earth PA ESR retains singlet

Lorentz lineshape and g factor constant until I2 dopant concentration >2mol%

at which doped level the ESR signal disappeared.