Melamine (MEL) is commonly used in kitchen utensils and flooring materials in our daily life. However, it can easily melt in accidental fires and cause property damage because the fire does not extinguish. Therefore, a flame retardant (FR) is needed. Herein, we designed a thermostable and inflammable melamine plastic by introducing hydroxy functionalized tris(2-chloroehtyl) phosphate (TCP-OH) FR. The direct flammability tests showed that MEL with TCP-OH group almost did not burn when exposed to the torch flames. MEL loses its existing shape and increases its volume, whereas MEL with TCP-OH does not lose shape even in the direct fire, also easily extinguished. Through the analysis of thermal decomposition, MEL with TCP-OH group exhibited distinguishably stable thermal behavior compared to MEL group, supporting the direct flammability test. These research result confirmed that MEL with TCP-OH groups enhanced thermal stability and flame retardancy, so it can be expected to be used as material to prevent spread of fire.