Abstract: Poly-ε-caprolactone(PCLs)was synthesized by ring-opening polymerization of ε-caprolactone initiated by caprylate stannous and was characterized with GPC,DSC,XRD and FT-IR respectively.PTC composite was prepared from mixing carbon black N990 and PCL and their microstructure,volume expansion and electrical properties were investigated.The results show that the number-average molecular weight(Mn),weight-average molecular weight(Mw)and polydispersity index(Mw/Mn)of PCL are 24175,38666 and 1.60.Its melting point is 62℃ and degree of crystallization is 42.48%.The percolation threshold of the PCL composites is 35%by weight and the PTC intensity are higher than two orders of magnitude.Carbon particles are dispersed uniformly in PCL matrix,mainly in form of aggregates.Curves of the logarithm of resistivity versus volume of N990/PCL composites indicate that volume expansion is only one of important factors of PTC effect.