Conductive polymer composites (CPCs) have attracted intensive attention for several decades because they can endow the materials with not only good processability but also various functionalities except the electrical conductivity. It is known that the electrical resistance of the CPCs is dominated by the conductive networks in the polymer matrix. Therefore, tiny change of the conductive networks can lead to remarkable changes in the output electrical signal of the CPCs. Utilizing this stimulus-response behavior of conductive networks to the environment conditions, CPCs can be used to design sensitive sensors to detect or monitor the environment conditions, such as the strain/stress, pressure, temperature, solvent or vapor. This review systematically outlines the preparation, microstructures, properties, and the stimulus-response mechanisms to the environment conditions of the CPCs as well as their applications in various sensitive sensors, including strain sensors, pressure sensors, liquid sensors, vapor sensors, and temperature sensors. Finally, the open question and future challenge of utilizing the stimulus-response behavior of CPCs to design versatile sensors are discussed.