A method for producing a cyclic olefin-based
copolymer, in which the cyclic olefin-based
copolymer includes (A) one or more repeating units derived from an olefin, (B) one or more repeating units derived from a cyclic non-
conjugated diene, and (C) one or more repeating units derived from a cyclic olefin, a
glass transition temperature of the cyclic olefin-based
copolymer measured by a differential scanning
calorimeter (DSC) is equal to or higher than 100°C, the method includes a
polymerization step of copolymerizing an olefin, a cyclic non-
conjugated diene, and a cyclic olefin in a presence of a catalyst for
olefin polymerization, containing a
transition metal compound (A) and a compound (B), the
transition metal compound (A) contains one or two or more selected from the group consisting of a
transition metal compound (A-1) and a transition
metal compound (A-2), and the compound (B) contains one or two or more selected from the group consisting of an organic
metal compound (B-1), an organic aluminum oxy compound (B-2), and a compound (B-3) that reacts with the transition
metal compound (A) to form an
ion pair.