A facile electrochemical functionalization method was utilized to decorate single-walled carbon nanotubes (SWNTs) with tin oxide and their gas sensing performance toward various analytes (NH₃, NO₂, H₂, H₂S, acetone, and water vapor) was evaluated at room temperature. Tin oxy-hydroxide was site-specifically precipitated on the surface of SWNTs because of an increase in local pH during electrochemical reduction of nitrate to nitrite ions. By adjusting the amount of charge passed during deposition, the amount of tin oxide deposited on SWNTs was controlled, which altered the electronic and gas sensing properties of the nanostructures. The resulting hybrid nanostructures showed excellent sensitivities upon exposure to trace amounts of both oxidizing gases (limit of detection (LOD) of 25 ppb_V for NO₂) and reducing gases (LOD of 10ppm_V for H₂) at room temperature. The enhanced sensing performance was due to the charge transfer between the surface active tin oxide nanoparticles and SWNTs, with the direction of charge transfer depending on the analyte gas. This approach can be applied to fabricate other hybrid metal oxide-SWNTs nanostructures to create highly sensitive gas sensor arrays.