One-dimensional gold nanorods can grow spontaneously in a surfactant solution. In this study, a mixture of hexadecyltrimethylammonium bromide ( HTAB) and octadecyltrimethylammonium bromide (OTAB) was used as a surfactant solution. When the solution gelled, high-aspect-ratio gold nanorods, with an average long-axis length of similar to 1100 nm and an aspect-ratio of similar to 50, were synthesized with a yield of similar to 90%, whereas no high-aspect-ratio gold nanorods were synthesized when the solution did not gel. This phenomenon indicates that there is a close relation between the gelation of a surfactant solution and the elongation of gold nanorods. (c) 2008 Elsevier B. V. All rights reserved.