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 LiPF6, 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 LiPF6 specifically shows fire-retardant. The thermogravimetric analysis also indicates that LiPF6 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.