Partitioning of 11 different proteins and 30 small organic compounds was examined in aqueous dextran–PEG–sodium/potassium phosphate buffer (0.01 M K/NaPB, pH 7.4) two-phase systems (ATPSs) containing 0.5 M sucrose or 0.5 M trehalose. The data obtained were compared to those reported previously for the same compounds and proteins in osmolyte-free ATPS and ATPS containing 0.5 M TMAO (Breydo et al. (2015) Archives of Biochemistry and Biophysics. in press), and analyzed in terms of the so-called Collander linear solvent regression relationship. It was found that the logarithms of the partition coefficients of proteins in the presence of 0.5 M sucrose and trehalose are linearly interrelated. The structural distances of protein 3D structures relative to that of ribonuclease B were estimated. These estimates were shown to be linearly related to the previously reported values determined for the same proteins based on their responses to different ionic environments.