Crystalline synthetic resin composition

A crystalline synthetic resin composition comprising 100 parts by weight of a crystalline synthetic resin selected from the group consisting of polyolefins, thermoplastic linear polyesters, polyphenylene sulfide, polycaprolactone and linear polyamides compounded with (a) 0.01 to 5 parts by weight of at least one selected from the group consisting of alkali metal carboxylates, alkali metal .beta.-diketonates and alkali metal salts of .beta.-ketoacetic esters and (b) 0.01 to 5 parts by weight of at least one of basic polyvalent metal salts of cyclic organophosphoric esters of the following formula (I):

• ##STR5## wherein R.sub.1 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R.sub.2 and R.sub.3 each represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, M represents a group III or IV metal atom of the periodic table, and X represent OH--when M represents a group III metal atom of the periodic table and X represents O.dbd. or (OH).sub.2 --when M represents a group IV metal atom of the periodic table.