The Sun is mostly made of two elementsA substance that is made of atoms with the same chemical properties, and which cannot be decomposed chemically into simpler substances., called Hydrogen and Helium, in a state of matter called plasmaPlasma consists of a gas heated to sufficiently high temperatures that the atoms ionize. The properties of the gas are controlled by electromagnetic forces among constituent ions and electrons, which results in a different type of behavior. Plasma is often considered the fourth state of matter (besides solid, liquid, and gas). Most of the matter in the Universe is in the plasma state..
To learn more about the Sun, please visit NASA and World Book or the Solar and Heliospheric Observatory.