Through the coordinative chain transfer copolymerization strategy, 1,3-butadiene/isoprene copolymers bearing exactly tunable molecular weights, narrow molecular weight distributions, and precisely controllable compositions are successfully achieved. Approximately 4-6 polymer chains can be produced per molecule of precatalyst Nd((OPr)-Pr-i)(3), revealing a higher atom-economic fashion than the traditional living copolymerization strategies. Detailed kinetic studies demonstrated living characteristics for the present system, and copolymer compositions agree well with feed ratios, suggesting the good controlling ability of the catalytic system. The monomer reactivity ratios were determined as r(BD) = 0.76 and r(IP) = 0.70, and NMR spectral analysis showed random sequences for the resultant copolymers.