Chlorine substitution reactions of dichlorotriphosphazatriene (PNC12)3 with nylon 6 in monochlorobenzene were studied under various experimental conditions. The extent of reaction was estimated with the weight method and HCI method. The reaction rate was increased with the increasing the concentration of reagent and increased in proportional to the reaction time. And also the molecular cross-linking was observed. The reaction of nylon 6 with (PNC12)3 was the approximately first order reaction on the concentration of (PNC12)3 and the activation energy of reaction was about 11.6 Kcal/mole.