Environmental pollutants, especially volatile organic compounds (VOCs), often cause some serious health issues, and hence it is imperative to monitor and prevent the leakage and diffusion of these vapors. Nanomaterial based sensors are powerful tools in environmental monitoring. Since carbon nanotubes tend to spontaneously aggregate and entangle together, resulting in heterogeneous dispersion and poor properties, it is necessary to find some methods to overcome this shortcoming and to fully exploit their applications. In this paper, a novel multiwall carbon nanotube graft polystyrene-block-poly(tert-butyl methacrylate) (MWNTs-g-PtBMA-b-PS) as a compatibilizer was designed and synthesized to construct polystyrene-block-poly(tert-butyl methacrylate)/MWNT (PS-b-PtBMA/MWNT) ternary conducting polymer nanocomposites and to fabricate into thin films to monitor chloroform vapor. The UV–vis, SEM and TEM investigations showed that the dispersion behavior of MWNTs was improved via incorporation of compatibilizer with various loading amounts. The nanocomposite thin films exhibited selective response to chloroform vapor, and the response patterns were influenced by the contents of compatibilizer and MWNTs and the analyte concentrations. The film sensors with compatibilizer exhibited excellent response, reproducibility and stability compared with those devoid of compatibilizer, and consequently they can be employed as a prospective candidate of chemical resistors or electronic noses for detection of chloroform vapor. Keywords: Carbon nanotubes, Smart materials, Polymer–matrix composites (PMCs), Electrical properties