Abstract: A flame-retardant polyester resin composition includes a thermoplastic polyester resin, between 1 to 30 wt. % of an organic halogenated flame-retardant, between 5 to 60 wt. % of an inorganic filler, and between 0.5 to 20 wt. % of a phosphoric ester of the following formula (1): ##STR1## wherein R represents a divalent organic group, R' which may be the same or different, is selected from C.sub.1 to C.sub.20 aliphatic groups, C.sub.3 to C.sub.13 alicyclic groups and C.sub.6 to C.sub.18 aromatic groups, m represents a number of 1 to 30, and n represents an integer of 0 to 3.