The measurements of thymidine absorbance in presence of SDS/solvent/water systems at 25°C by UV-Vis technique are reported. The solvents selected were the following aliphatic alcohols: ethanol, n-butanol, n-heptanol and n-decanol. In this paper first time are presented data for SDS micelles in alcohols with some addition of water. In all studied systems concentrations of SDS (sodium dodecyl sulphate) were above CMC. Water concentration in the studied systems was defined by R parameter according to relation: R= [H2O]/[AOT] and was between 0 to 50 depending on the system. In the present work SDS micelles mimicked in a very simple way the structural aspects of some domain in bio membranes. The distribution of thymidine, which is one of the pyrimidine bases of living matter (is found in the nucleic acid DNA) between organic and micellar phase was the object of our study. Using UV-Vis technique the investigation of thymidine/alcohol/SDS/water system at 25°C were done, and next the results were discussed in the context of influence an aliphatic alcohol on thymidine interaction with SDS micelles. Moreover, obtained results involve us to predict the privilege location of thymidine molecules in SDS micelles. The experimental values of thymidine absorbance as a function of surfactant concentration was analyzed with NLREG procedure. There were two adjusted parameters: the binding constant and distribution constant of thymidine partitioned between alcohol and SDS micellar phase, and finally on thymidine distribution between solvent and SDS micelles. Obtained results are discussed in the context of solvent influence on thymidine-SDS-alcohol-water system. The UV data showed the strong influence of the hydrocarbon chain length in alcohol and water concentration on the absorbance of thymidine in studied systems. The solvent influence on thymidine absorption results from the type of SDS micelles in the system. In ethanol and butanol SDS normal micelles are favoured; in heptanol and decanol SDS reversed micelles are more probable. There was found that thymidine molecules interact stronger with SDS micelles in decanol in comparison to shorter alcohols. Such tendency is probably connected with different type of micelles (normal or reversed) existing in studied solvents: short and long aliphatic alcohols.