Hydrogels possess a three-dimensional network structure, exhibiting high water-retention capacity and excellent biocompatibility. Among them, poly(N-vinylcaprolactam) (PNVCL) nanogels have garnered significant attention as next-generation drug delivery systems due to their ability to undergo volume phase transitions within physiological temperature ranges, allowing for the precise control of drug release rates. In this study, nano-sized hydrogels were synthesized through an eco-friendly method by applying electron beam (EB) irradiation to aqueous solutions of N-vinylcaprolactam (NVCL) monomers or polymers without the use of chemical crosslinking agents. The concentrations of NVCL, PNVCL, and NIPAAm were varied within the range of 1–5 wt%, and the effects of crosslinking density were investigated at irradiation doses of 25 and 50 kGy. The chemical structure and physical properties of the synthesized hydrogel were analyzed with various analysis equipment.