What are elements in humans body?

Most of the human body is made up of water, H₂O, with cells consisting of 65-90% water by weight. Therefore, it isn't surprising that most of a human body's mass is oxygen. Carbon, the basic unit for organic molecules, comes in second. 99% of the mass of the human body is made up of just six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. You may also wish to view the element composition of an average human body by mass.

1. Oxygen (65%) 
2. Carbon (18%) 
3. Hydrogen (10%) 
4. Nitrogen (3%) 
5. Calcium (1.5%) 
6. Phosphorus (1.0%) 
7. Potassium (0.35%) 
8. Sulfur (0.25%) 
9. Sodium (0.15%) 
10. Magnesium (0.05%) 
11. Copper, Zinc, Selenium, Molybdenum, Fluorine, Chlorine, Iodine, Manganese, Cobalt, Iron (0.70%) 
12. Lithium, Strontium, Aluminum, Silicon, Lead, Vanadium, Arsenic, Bromine (trace amounts) 

Reference: H. A. Harper, V. W. Rodwell, P. A. Mayes, Review of Physiological Chemistry, 16th ed., Lange Medical Publications, Los Altos, California 1977.