The effect of temperature on the growth of the long axis of gold nanorods is studied. The length of the nanorods decreases gradually with an increase in the growth temperature. By considering the chemical equilibrium between hexadecyltrimethylammonium bromide (HTAB) micelles and Au ions, we suggest that the secondary nucleation of seeds in a growth solution affects the long-axis length. In addition, small-angle X-ray scattering suggests that the equilibrium self-assembled structure of surfactant molecules does not affect the long-axis length in the present system.