Provided is an electrostatic discharge (ESD) protection structure including a substrate, a pick-up region, a first MOS device, a second MOS device, a first doped region and a second doped region. The pick-up region is located in the substrate. The first MOS device has a first drain region of a first conductivity type located in the substrate. The second MOS device has a second drain region of the first conductivity type located in the substrate. The first drain region is closer to the pick up region than the second drain region is. The first doped region of a second conductivity type is located under the first doped region. The second doped region of the second conductivity type is located under the second doped region. The area and/or doping concentration of the first doped region is greater than that of the second doped region.