Abstract: Solubilization of nile red (NR) dye in aqueous solutions of tetradecyltrimethylammonium bromide (TB) was studied by spectrophotometric method. Experiments were carried out both with NR saturated solutions under conditions of thermodynamic equilibrium of the solution with a dye precipitate, and at an NR constant weight. The solubility of NR in water (about 2 μM) has been refined. Extinction coefficients of NR monomers in water and micellar surfactant solutions were found. The micellization critical concentration (CMC) of TB in the presence of NR was determined, and the theoretical conclusion about the decrease in the surfactant CMC under the action of solubilizate was confirmed. The solubilization thermodynamic parameters were calculated on the basis of the following experimental data: the solubilization capacity of micelles, the coefficient of the solubilizate distribution between micelles and the surrounding solution, and also the standard affinity of NR solubilization. The problem of molecular NR aggregation in water and aqueous solutions of TB was considered. It has been found that the rate of reaching aggregative equilibrium is much lower than the rate of NR dissolution, therefore published spectral data based on the presence of only NR monomers mostly refer to the insufficiently equilibrium cases. It is shown that the process of NR solubilization begins in the prеmicellar region of TB, but is most effective in the presence of micelles.