A method for producing a silicon-carbide nanostructure, which includes steps of: irradiating a carbon-source supplied to a reaction chamber at a pressure of 1. Pa to 70 Pa with microwaves of 0.5 kW to 3 kW; generating plasma in a space above the silicon substrate at a temperature of 350° C. to 600° C.; and forming a silicon-carbide nanostructure having cone-shaped silicon-carbide aggregates which are scattered on and protruded from a surface of a silicon substrate. The silicon-carbide aggregates have a crystal structure of 2H α-siC.