Polyester/cotton 65/35 blended fabric was treated with Pyrovatex-trimethylolmel-amine (TMM) and tetrabromobisphenol A (TBBA) by padding-drying-curing method varying the concentration of solution in 3 bath system. The optimum concentrations of Pyrovatex, TMM, and $H_3PO_4$ in the 1st bath were taken so that the P content in treated fabrics could be maximum. The optimum concentration of Pyrovatex in the 3rd bath to fix TBBA on fabrics as much as possible was investigated. Flame retardancy of fabrics treated with the mixture of P compound and Br compound was found to be superior to that treated with each compound alone. Polyester/cotton 65/35 blended fabric was treated with Pyrovatex-TMM/TBBA compounds in 3 bath system showed self-extinguishing properties and their LOI was above 27. Flame retardant mechanism was discussed by thermogravimetric analysis. The flame-retardants of Pyrovatex-TMM/TBBA treated for polyester/cotton 65/35 blended fabrics were found to act mainly by a condensed phase mechanism.