Solid polymer electrolytes (SPEs) comprising crosslinking agent and plasticizer based on natural resources, tannic acid (TA), were prepared by facile one-pot ultraviolet (UV) light induced polymerization for all-solid-state lithium-ion battery applications. Poly(ethylene glycol) methyl ether methacrylate (PEGMA) as an ion-conducting unit and methacrylated TA (MTA) as a crosslinking agent are copolymerized in the presence of poly(ethylene glycol)-grafted TA (PTA) as a plasticizer. Dimensionally stable free-standing SPEs are obtained with the incorporation of very small amount, 0.1 wt%, of MTA compared to that of the PEGMA due to high crosslinking efficiency of the MTA. When 2.0 wt% of PTA with wax state having ion-conducting chain is added, maximum ionic conductivity of 5.6 x 10^-4 S/cm at 30 ^oC is obtained which is one magnitude larger than that of the waxy P(PEGMA) without any crosslinking agent.