Small-angle X-ray scattering (SAXS) study on supercritical cyclohexane was made to obtain density fluctuation and correlation length, which are quantitative expressions for structural fluctuation. The measurements were carried out along three isothermal conditions at the reduced temperatures of T-r =T/T-c = 1.02, 1.04 and 1.06. The SAXS measurements for supercritical benzene were also carried out as a reference to estimate absolute values of the density fluctuation for supercritical cyclohexane. The density fluctuation and the correlation length for cyclohexane were compared with those for CO2, CHF3, C2H4 and benzene, which were already reported, focusing on the differences of intermolecular interaction and the molecular size. (c) 2007 Elsevier B.V. All rights reserved.