The study of the properties of nanoclusters is important from various fundamental and applications points of view. A comparative study of the frontier orbitals, and the molecular electrostatic potential (MEP) surfaces of the oxygen nano clusters O4 and O8 has been carried out using first principles. The lower value of the frontier orbital energy gap in the case of O8 makes it a softer molecule as compared to O4. The difference in the MEP surfaces clearly predicts the difference in the active sites for electrophilic and nucleophilic interactions in the case of the two clusters.