The positive temperature coefficient (PTC) behavior of a conductive Nylon/Carbon black (CB) composite was investigated. The Nylon/CB composite was irradiated with gamma rays to a dosage of 50, 100, and 150 kGy for the purpose of reducing the negative temperature coefficient (NTC) of conductive composite. It was found that the PTC temperature depended on the melting point of polymer, and that the PTC intensity of Nylon/CB increased as particle size of the carbon black decreased. The electrical reproducibility of Nylon/CB was improved by radiation crosslinking compared with the unirradiated compound. The absence of the NTC effect in the crosslinked CB-filled polymer composites was related to an increase in the viscosity of the polymer matrix, thereby leading to a significant reduction in the mobility of the CB particles in the composites.