ALTERNATING COPOLYMERS OF A CONJUGATED DIENE WITH A CONJUGATED POLAR ETHYLENICALLY UNSAURATED MONOMER, WHEREIN THE CONJUGATED DIENE UNIT AND THE CONJUGATED POLAR ETHYLENICALLY UNSATURATED MONOMER UNIT ARE BONDED SUBSTTANTIALLY ALTERNATELY, ARE PRODUCED BY COPOLYMERIZING SAID CONJUGATED DIENE WITH SAID CONJUGATED POLAR ETHYLENICALLY UNSAURATED MONOMER BY MEANS OF A CATALYST PREPARED FROM A COMPONENT (A) OF A COMPOUND OF A TRANSITION METAL OF THE GROUP IV OR V IN THE PERIODIC TABLE, PROVIDED THAT THE CHELATE COMPOUNDS ARE EXCEPTED, AND A COMPONENT (B) OF ZINC HALIDE OR AN ALUMINUM COMPOUND CONTAINING HALOGEN. THIS COPOLYMERIZATION ACTIVITY CAN BE IMPROVED BY ADDING A COMPONENT (C) OF A RADICAL INITIATOR SELECTED FROM THE GROUP CONSISTING OF ORGANIC PEROXIDES, AZONITRILE COMPOUNDS AND TRIALKYLBORON-OXYGEN SYSTEM TO THE AOVE DESCRIBED COMPONENTS (A) AND (B). FURTHERMORE, THE MOLECULAR WEIGHT OF THE ALTERNATING CO POLYMER CAN BE ADJUSTED BY ADDING A MOLECULAR WEIGHT REGULATOR SELECTED FROM THE GROUP CONSISTING OF MERCAPTANS AND CARBON POLYHALIDES CONTAINING BROMINE OR IODINE AS AN ESSENTIAL COMPONENT TO THE POLYMERIZATION REACTION SYSTEM.