The objective of this work is to examine whether the various UNIFAC models can represent phase behavior of biochemicals in the dilution solution such as partition coefficients (log P-i). Especially, the log P-i of a solute in the n-octanol/water system was used as main target for the examination in this work. First, the log P-i of common chemical solutes was tested by use of various UNIFAC models. It was concluded that the original model and Larsen et al.＇s model [B.L. Larsen, P. Rasmussen, Aa. Fredenslund, Ind. Eng. Chem. Res., 26 (1987) 2274-2286] were suitable for the prediction of the log P-i. In the next, both models were applied to calculation of log P-i of biochemicals such as amino acids, their derivatives, and sugars. In addition, hydrophobicity constants (pi) of an amino acid side chains were calculated from the log P-i of amino acids. From the above results, the performance of the UNIFAC models for log P-i and pi was discussed.