Abstract: The metal-nonmetal transition of metallic wires driven by pulsed current is very important for understanding the evolution of plasma electrothermal instability. The metal-nonmetal transition in aluminum wire and coated aluminum wire under nanosecond pulsed current was investigated with optical diagnostic of high spatiotemporal resolution and magnetohydrodynamic simulation. The transition of aluminum wire from metallic state to nonmetallic state, as well as the most unstable state of electrothermal instability for aluminum wire, were analyzed based on Ioffel- Regel condition, metallization theory and the dependence of resistivity with respect to temperature. The bare and coated aluminum wires share common phase transition in the initial stage of the discharge with occurrence of stratified structures induced by electrothermal instability. The wire resistivity outclasses the maximum metallic resistivity for standard metals at the instant of voltage breakdown. The aluminum wires accomplish metal-nonmetal transition before the instant of voltage breakdown. The research provides the foundation for investigation on electrothermal instability in metallic load driven by pulsed current.