Abstract: A conductive polymer composition having PTC characteristics comprising a polymer matrix, constituting from 20 to 98 percent by weight of the composition, throughout which is dispersed a mixture of conductive carbon blacks constituting from 2 to 80 percent by weight of the composition, the mixture comprising a first conductive carbon black and a second conductive carbon black, each of the carbon blacks having a structure level, as measured by DBP technique, of 40 to 150 cc/100 g and each constitutes from 1 to 40 percent by weight of the composition, the first carbon black comprising particles having average size in the range from 35 to 300 nm and the second carbon black comprising particles having average size in the range from 15 to 25 nm.