PURPOSE: To provide a cycloolefin copolymer comprising polymer units from a polycyclic olefin and other polymer units, containing repeating structural units having a plurality of electron-withdrawing groups, having specified properties, being excellent in transparency, adhesion, dimensional stability, hardness, and hydrolysis resistance and being useful for coating materials, etc.

CONSTITUTION: There is provided the objective cycloolefin copolymer having (A) at least one polymer unit of a polycyclic olefin such as a compound of the formula (wherein R1 to R4 are each H, a 1-20C hydrocarbon group or the like, (B) at least one polymer unit of an olefin, such as hexa-1,5-diene or the like, containing at least one double bond, and, optionally, (C) at least one polymer unit of an acyclic monoolefin such as ethylene, having a solution viscosity (η) of below 0.25 dl/g, an equivalent weight, based on the olefinic double bond, equal to or lower than the number-average molecular weight, and containing at least one recurring structure having at least two electron-withdrawing groups such as carbonyl groups. It is desirable that the copolymer has a compositional ratio of 10-90 wt.% component A, 2-30 wt.% component B, and 2-50 wt.% component C.