A novel fire-retardant gel electrolyte with flammable solvents has been achieved for use with lithium batteries. We report that by optimizing of the ratio of polyacrylonitrile, ethylene carbonate, propylene carbonate, and LiPF 6 , the gel electrolyte shows a remarkable fire-retardance without the need to add commercial reagents for fire-retardant property. The linear burning ratios determined by a burning test with a butane-gas burner indicate that the burning behavior of the gel electrolyte strongly depends on the host polymer and lithium salt used; the PAN-based gel electrolyte containing LiPF 6 specifically shows fire-retardant. The thermogravimetric analysis also indicates that LiPF 6 lowers the carbonizing point of the PAN-based gel electrolyte and increases a residue of a carbonaceous material remaining after burning. The correlation of the linear burning rates and the carbonizing points suggests that the fire-retardant property of the PAN-based gel electrolyte results from the carbonaceous layer formed on the surface.