Disclosed herein is a fire retardant treatment method using water glass. According to the fire retardant treatment method of the present invention, water glass having excellent fire retardant effects without posing any risk to humans is used as a fire retardant, and imparts more durable fire retardancy to various substrates such as fibers, fabrics, non-woven fabrics, sheets, papers and the like. The fire retardant treatment method comprises the steps of: treating a substrate with water glass as a fire retardant by a spraying, dipping or application process; treating the water glass-treated substrate with a treatment agent to chemically solidify the water glass and impart lipophilicity to the water glass, the treatment agent including at least one modifier selected from C1-8 alcohols, ketones and ethers and an acid capable of inducing a polymerization reaction of silica; and drying the resulting material to evaporate water. |