In this study, flame retardancy properties of fabrics treated with phosphorous (P) doped and undoped SiO2 thin films were developed by sol-gel technique. As to this aim, P-doped and undoped SiO2 film were coated on cotton fabric from the solutions prepared from P, Si-based precursors, solvent, and chelating agent at low temperature in air using sol-gel technique. To determine solution characteristics, which affect thin film structure, turbidity, pH values, and rheological properties of the prepared solutions were measured using a turbidimeter, a pH meter, and a rheometer machines before coating process. The thermal, structural, and microstructural characterization of the coating were done using differential thermal analysis/ thermograviometry, fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy. In addition, tensile strength, wash fastness, flame retandancy, and lightness properties of the coated fabrics were determined. To compensate the slight loss of tensile strength of samples, which occurred at the treated fabrics with P-doped Si-based solutions, the cotton fabrics were coated with polyurethane films during second step. In conclusion, the flame retardant cotton fabric with durability of washing as halogen-free without requiring after treatment with formaldehyde was fabricated using sol-gel processing for the first time. Moreover the cotton fabrics, which were treated with P-doped Si-based solutions and then coated with polyurethane at second step, still has got nonflammable property. (c) 2007 Wiley Periodicals, Inc.