How many quarks are in a proton? How many quarks are in a neutron? Protons and neutrons each contain three quarks. A proton is composed of two 'Up' quarks and one 'Down' quark while neutrons are composed of one 'Up' quark and two 'Down' quarks. Author: Steve Gagnon, Science Education Specialist (Other answers by Steve Gagnon) Related Pages: All About Atoms