||Two kinds of carbon based nanofillers, carbon black (CB) and acetylene black (AB), a special subtype of carbon black, were each studied as a secondary nanofiller in polypropylene (PP) composite that contains single-walled carbon nanotube (CNT) as a primary nanofiller to explore the effect on electrical property. CB clusters and fibrous CNTs each can improve electrical conductivities of composites by forming conductive networks over short distances and long distances, respectively. Moreover, CB clusters and CNTs together have synergistic effect on the conductivity as CB clusters link the fibrous CNTs over small distances. Different compositions of CNT/CB pair and CNT/AB pair with a fixed total filler concentration of 1.4wt% were prepared by melt compounding/extrusion process with controlled residence time of 20mins. The effects of CB and AB as a secondary nanofiller were evaluated in terms of electrical conductivity, mechanical, rheological and morphological properties.