The most abundant element in the human body by number of atoms- hydrogen by weight - oxygen The most abundant element in the human body is <b>oxygen</b>. About two thirds (65%) of the human body is oxygen by mass. The most abundant metal in the human body is calcium. The most abundant element in the human body by number of atoms- hydrogen by weight - oxygen The most abundant element in the human body is <b>oxygen</b>. About two thirds (65%) of the human body is oxygen by mass.