A radial-leaded over-current protection device comprises a PTC element, a first electrode lead, a second electrode lead and an electrically insulating encapsulation layer. The PTC element comprises a first conductive layer, a second conductive layer and a PTC material layer laminated therebetween. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein. The first electrode lead has an end connecting to the first conductive layer, whereas the second electrode lead has an end connecting to the second conductive layer. The electrically insulating encapsulation layer includes a fluorine-containing polymer, and wraps around an entire outer surface of the PTC element and the ends of the first and second electrodes connecting to the PTC element. The electrically insulating encapsulation layer has a thickness of 102˜105 nm, and the radial-leaded over-current protection device has an initial resistance Rbf of 0.0017˜0.0027Ω.