On a metal wire with a self-healing function of a crack using electric field trapping of metal nanoparticles, we examined a healable crack width by using the different particle size. The electric field trapping is a phenomenon where the nanoparticles are trapped in the crack by the electric field in the region of the crack only, when a voltage is applied to the cracked wire covered with the nanoparticle solution. In this paper, first, we theoretically analyzed and calculated the particle size dependence of forces acting on the nanoparticles. Next, we fabricated gold wires with patterned cracks on a glass substrate, and measured the healable crack width by comparing 20 nm, 100 nm and 200 nm in particle radius. In the experiments, gold nanoparticles aqueous solution was used as nanoparticles solution. As a result, in the each case of 20 nm, 100 nm and 200 nm in particle radius, cracks up to 1.5 μm, 2.5 μm and 4.0 μm were successfully healed by applying less than 4.2 V in amplitude and 100 kHz in frequency of AC voltage, respectively. These results indicate that the larger nanoparticle can heal the wider crack with the same cross-sectional shape of the wire and the approximately same applied voltage. After the experiments, we confirmed that assembled nanoparticles were bridging the crack at the inside of the crack through scanning electron microscope (SEM) observations.