Electrical conductive polymer composites (CPCs) are good candidates as chemiresistors due to their tunable conductivity and good processability. They have great potential in monitoring of human being health and environment contaminants. Herein, melt-mixed blends of poly(vinylidene fluoride) (PVDF) with polycarbonate (PC) were filled with multi-walled carbon nanotubes (MWCNTs) were fabricated. By choosing different PC types, the viscosity of the system was varied. A co-continuous structure was formed when PC/PVDF blend ratio was 40w/60w, and MWCNTs were selectively localized in the PC component. CPCs containing low viscous PC exhibited highest conductivity which was attributed to the best dispersion of the MWCNTs in the PC matrix. In the following, vapor sensing behaviors of CPCs towards good vapors such as dichloromethane, acetone, tetrahydrofuran, and ethyl acetate were investigated. Cyclic sensing tests indicated that CPCs containing low viscous PC exhibit lowest sensitivity, but a good reversibility because of good filler dispersion. As expected, MWCNT loading is an important factor for controlling the sensitivity of CPCs, i.e., low MWCNT loading led to higher relative resistance changes of CPCs. To further investigate the relationship of filler localization and vapor sensing behaviors, the PC component of CPCs was extracted by dichloromethane. Scanning electron microscopy (SEM) images revealed that there were some remaining MWCNTs at the surface of the remaining non-soluble PVDF. Also these open porous CPCs devoid of the PC component are sensible to vapors. However, a different sensing tendency was observed compared to those solid CPCs. The system where the low viscous PC was extracted exhibited the highest sensitivity towards organic vapors, which was attributed to different sensing mechanisms. This study provides new thoughts in preparation, characterization, and application of chemiresistors.