Disclosed are a memristor device, a method of fabricating the same, a synaptic device including a memristor device, and a neuromorphic device including a synaptic device. The disclosed memristor device may comprise a first electrode, a second electrode disposed to be spaced apart from the first electrode; and a resistance changing layer including a copolymer between the first electrode and the second electrode. The copolymer may be a copolymer of a first monomer and a second monomer, and the first polymer formed from the first monomer may have a property that diffusion of metal ions is faster than that of the second polymer formed from the second monomer. The second polymer may have a lower diffusivity of metal ions as compared with the first polymer. The first monomer may include vinylimidazole (VI). The second monomer may include 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3D3). The copolymer may include p(V3D3-co-VI).