This work reports the first successful synthesis of polycaprolactone (PCL)-based degradable ionomers using free-radical chemistry. Degradable cationic ionomers were synthesized by random radical terpolymerization of 2-methylene-1,3-dioxepane (MDO), methyl methacrylate (MMA), and N,N-dimethylaminoethyl methacrylate (DMAEMA) and followed by quaternization of amine with alkyl bromide. The terpolymerization of MDO, MMA, and DMAEMA led to a polymer with ester group randomly distributed in the polymer chains. The small-angle X-ray scattering (SAXS) analysis, the transmission electron microscope (TEM), and dynamic mechanical analysis (DMA) showed ionic aggregates existing in ionomers. Ionomers quaternized by ethyl bromide showed relative strong ionic interaction and showed aggregates with a diameter around 30 nm, which had a separate glass transition temperature (T-g) and performed rather as filler material. Ionomers containing 40 mol % of ester group and 20 mol % of ionic group showed biodegradability after being buried in compost.