We used density functional theory studies (DFT) in terms of energetic and electronic properties to assess the aptitude of polypyrrole fragment (3PPy) as a gas sensor towards SO2, NH3, H2O, CO, CH4 and CO2. By using B3LYP/ 6-31G(d) level of theory, the sensitivity along with selectivity of 3PPy among SO2, NH3, H2O, CO, CH4 and CO2 were considered in this study. The finding shows that a large interaction energy in 3PPy-NH3 (30.58 kJ/mole) and 3PPy-H2O (27.78 kJ/mole) and somewhat in 3PPy-SO2 (18.34kJ/mole) complexes are given compared to less interaction energies in 3PPy-CO (5.29 kJ/mole), 3PPy-CO2 (5.25 kJ/mole) and 3PPy-CH4 (0.11 kJ/mole) complexes. To further understand the electronic properties of 3PPy-X structures, Natural bond orbital charge distribution and the density of states (DOS) were calculated for the isolated 3PPy as well as different 3PPy-X complexes. The type of interaction between mentioned spices with 3PPy was studied with understanding the HOMO and LUMO energies. UV-vis spectra analysis was used for all 3PPy- X along with isolated 3PPy and related spectra show that the λmax values are red or blue shifted depend on the kind of complex which is the proof of interaction between 3PPy and mentioned spices.