A system in package structure and an electrostatic discharge protection structure thereof are provided. The electrostatic discharge protection structure includes a redistribution layer and a first transistor array. The redistribution layer has a first electrode and a second electrode. The first transistor array is coupled to a pin end of at least one integrated circuit, the first electrode and the second electrode. The first transistor array has a plurality of transistors. A plurality of first transistors of the transistors are coupled in parallel, and a plurality of second transistors of the transistors are coupled in parallel. The first transistors and the second transistors are configured to be turned on for dissipating an electrostatic discharge current.