We report comparative study of ozone adsorption on pristine Single Walled Carbon Nanotube (SWCNT) (8, 0) and Silicon doped Single walled Carbon Nanotube (Si – SWCNT) by density functional theory calculations based on DeMol3 code. Importance is given to the effects of silicon doping in carbon nanotube for comparative study of adsorption of ozone. The results show that silicon doping keeps the semiconducting character of pure carbon nanotubes with reduction in band gap from 0.71 eV to 0.54 eV. The ozone gas molecule is physisorbed with binding energy 0.431eV and minute charge transfer of 0.013 e from pure carbon nanotube, consistent with the strong oxidizing nature of ozone. The binding energy and charge transfer indicate that the ozone adsorption on pure carbon nanotube is gentle and reversible. However, when ozone adsorbs on silicon doped carbon nanotube, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a Si-O σ bond with binding energy 3.902 eV and charge transfer of 0.252 e. The band structure and density of states shows that the occupancy state in valence band near Fermi energy is completely altered due to ozone adsorption. The charge density analysis also shows formation of sigma bond between silicon and oxygen atoms. The charge density iso-surface shows the oxidation of silicon atom and dissociation of ozone molecule into silicon - oxide and releasing of oxygen molecule.