Coenzyme Q10 (CoQ10) is an essential cofactor of the electron transport chain which plays a pivotal role to supply energy for chemical reactions in the body, and a lipophilic antioxidant component of the lipid membranes that surround all cells and the various organelles such as microsomes and mitochondria. Even though the antioxidants are produced by the body, their blood level is reduced by aging, lifestyle and environmental factors. As a well-established antioxidant, CoQ10 participates in electron and proton transport of the respiratory chain in the mitochondrial inner membrane and decreases oxidative stress and prevents free radical oxidation of the cells and tissues. In number of trials, potential usefulness of CoQ10 have been shown in mitochondrial disorders and variety of diseases progressed by due to oxidative stress and decreased antioxidant capacity. We have explored CoQ10’s cellular bioenergetic activity and antioxidant properties, and its functions for common clinical conditions such as cardiovascular and neurodegenerative diseases, cancer, diabetes, and renal failure in our examination.