A fabric is provided that has high degree of flame resistance in the case of a union fabric consisting of a halogen-containing flame resistant fiber including antimony compounds, and a cellulosic fiber, and the fabric is classified into class M1 of NF P 92-503 combustion test in France. A flame resistant union fabric obtained by co-weaving: (A) a fiber yarn 30% to 70% that has, as a principal component, a halogen-containing flame resistant fiber including an antimony compound 25 parts to 50 parts in an acrylic based copolymer 100 parts consisting of acrylonitrile 30% to 70% by weight, a halogen containing vinyl based monomer 30% to 70%, and a vinyl based monomer copolymerizable therewith 0% to 10%; and (B) a compound yarn 70% to 30% consisting of a cellulosic fiber (b-1) and a fiber melting at temperatures of 200 degrees C. to 400 degrees C. (b-2).