The efforts of bromine containing ale retardants on the polymerization of styrene have been studied. With the addition of fire retardant, rate of polymerization was not affected but molecular weight of polystyrene was decreased considerably. Since these results were considered on account of chain transfer to fire retardant molecules, the chain transfer constant of each fire retardant was determined on the styrene polymerization initiated by 2,2''-azobisisobuty-ronitrile at 60℃. Thechain transfer constants obtained are as follows ; 4,4''-isopropylidenebis (2,6-dibromophenol) : 129.0×10^-4, hexabronlodipheny1 oxide: 61.3×10^{-4, octabromodiphenyl oxide: 127.7×10-4, 2,4,6-tribromopheny1 1,3-dibramoisobutyl ether: 55.1×10-4 hexabromocy-clodcdecane: 21.5×10-4, his (2,3-dibromopropy1) dichloropropyl phosphate: 19.6×10-4 tris(2,3-dibromopropy1) phosphate: 11.9×10-4. These values were compared with each other and the reactivity of ale retardants was discussed on the view of their molecular structure.}