The aim of this work is evaluation of nano-particles Mg(OH)2 as flame retardant for fabricated cotton (cotton/PET/50/50). The native samples and that treated with Mg(OH)2 were characterized by using Infrared (IR) absorption and the Scanning Electron Microscope (SEM). The Mg(OH)2 nano-particles were incorporated into the fabricated cotton by curing different steps. The appearance of the absorption IR bands at 1443, 1631 cm-1 which specified the Mg-O bands of Mg(OH)2 unit indicated that Mg(OH)2 nano-particles are incorporated into the cellulosic chains. On the other hand, the morphology of the studied samples showed that the treated sample with Mg(OH)2 and the cured temperature not effect on the structure of the native sample. The thermal stabilities of the native and the treated samples were studied. The Thermo-gravimetric (TG) curves showed that a small changes had been appeared by treating cotton/PET fabric with Mg(OH)2 nano-particles. The curves showed that the treated sample cured at 160oC exhibited less weight loss; this means that this sample is more thermally stable than the other samples. The flammability of the samples was carried out using Limiting Oxygen Index (LOI). The results of the examination show that the value of LOI increases from 20.2 to 23.1 for the sample cured at 160oC. This indicated that Mg(OH)2 can be used as flame retardant for cotton/PET when cured at 160oC.