This study is based on comparison of the quality of well water before and after ozonation. The study was conducted in eight different sites of Bhaktapur Municipality in November 2016 to February 2017. Different water quality parameters such as Temperature, pH, Electric Conductivity, Dissolved Oxygen, BOD, Total hardness, Ca-hardness, Mg-hardness, Iron, Total coliform, Fecal coliform and Non-coliform were analyzed. The study determined physico-chemical and microbial quality of well water sources before and after treatment. There were no significant changes in conductivity of water from eight different sources before and after treatment. Conductivity values remained stable before and after treatment. pH of water after treatment varied slightly with respect to pH of untreated water. DO of all samples increased significantly after ozonation. BOD of samples decreased after ozonation. There was overall decrease in Total hardness, Magnesium hardness and Calcium hardness after treatment. Iron in its ferrous state had charge of 2+. When ozone was passed through the solution containing ferrous salts, it contributed oxygen atom that reacted with Fe2+ resulted to ferric salt and hence concentration of Fe²⁺ decreased. There was overall decrease in microbial parameters (Total coliform, Fecal coliform and Non-coliform).