The influences of the initial monomer concentration，catalyst concentration and polymerization temperature on the molecular weight of polybutadiene have been studied．It was found that the reciprocal of degree of polymerization(DP)gave linear relation-ships with [monomer]-1，[CoCl2·C5H5N4]1-2 and [Et2AlCl]1-2． From the temperature de-pendence of DP an activation energy for the chain termination of ca．14 kcal／mole was obtained．From the studies of the effect of adding some electron—donor compounds and heptane during polymerization on the molecular weight of polymer，linear relations be-tween DP-1 and [electron-donor] or [heptane] were obtained．If the slope of these straight lines could be regarded as chain transfer coefficient

then the values obtained are 1．87，0.36，0.19，0.14 and 0.0012 for triethylamine，tetrahydrofuran，pyridine，ethylthio-ether and heptane respectively．