The aim of this study was to investigate the effect of calcium hypophosphite (CaHP) and magnesium hypophosphite (MgHP) on the thermal stability and fire retardant properties of cotton fabrics. The effects of water-soluble nanoparticles, namely Na-montmorillonite and octaammonium polyhedral oligomeric silsesquioxane (OA-POSS), in the presence of CaHP were also investigated. The characterizations of flame-retardant-treated cotton fabrics were performed using thermogravimetric analysis, limiting oxygen index (LOI) and mass loss calorimeter studies. The residues remained after mass loss calorimeter test were characterized by conducting attenuated total reflectance Fourier-transform infrared spectroscopy and scanning electron microscopy with a wavelength-dispersive X-ray spectrometer. The results showed that the fire performance of cotton fabric increased as the treated amount of both hypophosphite compounds increased. CaHP showed better fire performance than MgHP. The fire retardant performance of CaHP was further improved when used with nanoparticles. The highest LOI value of 24.2 and the lowest peak heat release rate (PHRR) of 43 +/- 3 kW m(-2) were achieved with the use of CaHP and OA-POSS at a ratio of 19:1.