This study has been designed to investigate the following subjects of polyester fabrics finished with bromine and phosphorus-containing flame retardants: a) flame retardancy b) Synergistic effect of bromine and phosphorus on flame retardancy c) relationship between LOI, bromine and phosphorus contents. Treated fabric containing 3.2% bromine, 0.2% phosphorus or 2.5% bromine, 2.0% phosphorus satisfies the requirements of self-extinguishing Property. It is found that the effect of bromine at fixed phosphorus contents plays an important role in increasing flame retardancy. Relationship between LOI, bromine and phosphorus in this study can be expressed by the following equation. -ln｜S｜=${alpha}$-${eta}$/LOI or LOI=${eta}$/ln｜S｜/1+${alpha}$/ln｜S｜ where S: slope of P/Br atom ratio to bromine content at specific LOI levels ${alpha}$: intercept on the -ln ｜S｜ axis ${eta}$: slope of -ln ｜S｜ to 1/LOI