The paper presents the results of electrochemical and conductometric studies of poly (3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and composite material PEDOT:PSS/oriented nickel fibers in the presence of carbon dioxide. It has been shown that the introduction of oriented nickel fibers into the PEDOT:PSS polymer matrix improves the electrochemical properties of the polymer. The nickel fibers in the polymer bulk act as a catalyst and thus shift the PEDOT:PSS reduction peak towards positive potentials. Gas sensing elements for a conductometric sensor were fabricated by depositing PEDOT:PSS and composite films PEDOT:PSS/oriented nickel fibers on the surface of a glass substrate with interdigitated gold electrodes. Special equipment was designed to study the sensory properties of gas-sensitive elements. Using this equipment, we measured the sensory response Rr and the response time \(\tau\)0.9 of finished gas-sensitive elements in a carbon dioxide environment. Conductometric studies have shown that the response time \(\tau\)0.9 of the composite material to CO2 is shorter, and the sensory response Rr is twice as long as compared to a pure PEDOT:PSS film. As a result of the generalization of the experimental data, the possibility of using the composite material PEDOT-PSS/oriented nickel fibers to create electrochemical and conductometric sensors for carbon dioxide was shown.