Transparent polymers possessing excellent optical properties have attracted significant attention due to their wide-ranging applications in optical fibers, camera lenses, displays, and optical storage devices. Among the transparent polymers, cyclic olefin polymers (COPs) stand out for their exceptional transparency, high thermal stability, good chemical resistance, and low birefringence. Herein, we report the ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) containing an epoxy functional group (eDCPD) and their transformation to hydroxy functionalized COPs. The epoxy functional group was introduced into an allylic position of the cyclopentene ring not only to prevent crosslink reactions during the polymerization of DCPD but also for further transformation to other functional groups. Introducing polar functional groups into COPs is expected to improve the physical properties of COPs, such as adhesion and compatibility with other materials.