For the first time, a metal was introduced into the structure of the flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). A novel metal-organic composite, DOPO-Mg, was synthesized upon the reaction between melt DOPO and activated magnesium powder. The results show that DOPO-Mg has a high initial thermal decomposition temperature of up to 400 degrees C (5%). In addition, it was an amorphous-like material with minimal water absorption, which decomposed without a melting point. The product after the combustion of DOPO-Mg was magnesium pyrophosphate.