The synergistic role between phosphorus and nitrogen in flame retardant cellulose finished with Fyrol 76 and N-methylol acrylamide was confirmed. The degree of synergistic effect depends on mixing ratio of Fyrol 76 and N-methylol acrylamide, and there is optimum condition in mixing of flame retardant finishing agents. For the pass to DOC FF 3-71, about 30 mg phosphorus and 9 mg nitrogen per gram of dried flame retardant cotton is reguired and the value of limited oxygen index is to be over 27.5. The flame retardancy of finished fabric is durable to laundering and it is considered to be referred by the formation of vinyl polymer in amorphous region of cellulose.