Raman OH stretching frequency shifts in supercritical water and in O-2-or acetone- aqueous solutions near the water critical point were observed to discuss the microscopic solution structure of these fluids. In neat water, the peak frequencies shifted almost linearly to the density except near the critical density. As the temperature approached the critical temperature, the density dependence of the shift became non-linear. This behavior was considered to be due to some microscopic structural non-uniformity caused by the density fluctuation. In the solutions, such non-linear density dependences were decreased, suggesting the decrease in the local density augmentation around water molecules. (c) 2009 Elsevier B.V. All rights reserved.