A method for manufacturing metal nanorods includes: a step of adding a reducing agent to a metallic salt solution; a step of radiating light into the metallic salt solution containing the reducing agent; and a step of leaving the light-radiated metallic salt solution containing the reducing agent stationary in a dark place so as to grow metal nanorods. Metal nanorods can be also grown by forming a mixed solution by fractionating the above light-radiated metallic salt solution and mixing the fractionated metallic salt solution into a non-radiated metallic salt solution containing the reducing agent, or mixing a non-radiated metallic salt solution and the reducing agent into the above light-radiated metallic salt solution; and leaving the mixed solution stationary in a dark place so as to grow metal nanorods.