In this manuscript, cobalt complexes Col, Co2, and Co3 supported by PN3-type of ligand have been prepared, characterized, and applied in polymerization of myrcene (My), butadiene (Bd), and isoprene (Ip). The type of catalyst, cocatalyst, and temperature variation have little influence on polymer microstructure. We also have reported the preparation of novel isoprene myrcene copolymers in the presence of complex Col. Isoprene and myrcene are found to be randomly copolymerized at various monomer feeding, with typical myrcene incorporation of 7.6-57.6%. The copolymer has cis-1,4 microstructure of 69.4-73.4% and 79.4-83.4% for polyisoprene and polymyrcene segments, respectively, and T-g = ca. -41.7 to 51.1 degrees C. The reactivity ratios obtained from the Fineman-Ross plot of r(1) = 0.74 and r(2) = 1.67 (r(1) = k(mymy)/k(myip) and r(2) = k(ipip)/k(ipmy)) indicate that isoprene has the privilege of getting into the macromolecules during the polymerization by this catalyst system.