Continuous production of highly crystalline ZnO nanorods by supercritical hydrothermal synthesis was reported in this article. Zinc nitrate aqueous solution was pressurized to 30 MPa at room temperature and rapidly heated to 673 K by mixing with supercritical water and then fed into a tubular reactor. Residence time is about 10 s. Production of ZnO nanorod particles with uniform particle size distribution showed a strong ultraviolet light emission at room temperature. This article also reported in-situ surface modification of ZnO nanorods with organic reagents by the supercritical hydrothermal synthesis.