Abstract: A thermoplastic polymer composition of an aliphatic polyamide and a modifier. The modifier is a copolymer of nylon 6 and an acrylic polymer, its inclusion in the composition enabling the properties of the aliphatic polyamide (e.g. nylon 6, nylon 66, nylon 11) to be modified without need of co-condensation with the modifier.The modifier copolymer is 0.5 to 50 percent by weight of the composition. The proportion of acrylic polymer in the copolymer is not more than 25 percent by weight. The acrylic polymer comprises molecular chains derived from acrylonitrile or from a major proportion of an alkyl ester of acrylic or methacrylic acid and a minor proportion of a copolymerizable unsaturated carboxylic acid.The preferred acrylic polymer is a multi-phase polymer comprising a first, elastomeric, phase and a second, rigid thermoplastic, phase.The composition can be used for moulding articles.