Abstract: Flame retardant polyester compositions are provided which comprise melt blends of a synthetic linear polyester with up to about 25 percent, based on the weight of polyester, of a polyphosphate having the following formula: ##EQU1## WHEREIN Ar is a divalent radical having up to about 20 carbon atoms selected from arylene and haloarylene; R is a monovalent radical having up to about 20 carbon atoms selected from alkyl, aryl, haloalkyl and haloaryl; n is an integer greater than 1; and X is a monovalent radical selected from the group consisting of H, alkyl, aryl, haloalkyl and haloaryl, Y is a monovalent radical selected from the group consisting of H, OH and ##EQU2## where X and R are as above.