Designing sustainable epoxy resins with intrinsic recyclability and degradability has become vital in polymer science. Here, we report sulfur chain-modified epoxy networks (SxEyUz) through catalyst-free tri-component polymerization of elemental sulfur with glycidyl ethers of bio-sourced eugenol (EGE) and 10-undecenol (UGE) via inverse vulcanization. The biogenic allyl protons on EGE were disclosed to be critical for the dual-mechanism cross-linking system. Intermediates from the tri-component polymerization were found to be flowable, storable, and post-curable. Reprocessable epoxy polymers with tensile strength up to 13.0 MPa were obtained after curing, surpassing most reported bio-based polymers via inverse vulcanization. Carbon fiber (CF) composites fabricated in the SxEyUz matrix can be readily digested in a methanol solution of Na2S and neat hexylamine to recycle CF.