Along with industrial development, the demand for robust and portable sensors has been increasing over the past decade. Notably, current research has paid great attention on the design of miniature sensor based on nanoparticles. Graphene and polyaniline (PANI) are the two nanoparticles receiving intense research interest in this study field owing to their unique electrically conductive property. Fundamentally, the detection of pollutant using either graphene or PANI is following two simple steps, namely the exposure of the nano-sensor to the pollutant-containing environment, and monitoring of the change in electrical conductance of the nano-sensor. In this review, current application of graphene, PANI, and their nanocomposites on the detection of different types of pollutants was revisited. The latest developments regarding the nanoparticles, substrate, pollutant type, fabrication method, and performances were summarized and compared. Based on the summarized information, future directions in further advancing the application of these nano-sensors in the industry were proposed.