Abstract: Quantitative Structure-Property Relationship (QSPR) is a useful method in predicting physical and chemical properties based on the molecular structure, which has already been used in many fields successfully. In this paper, molecular connectivity indices combined with electronic parameter σ* were used to develop QSPR models for hydrophobicity (lgP) and acidity (pK_a) of 11 mono-carboxylic acids. The calculated values were of good consistency with the experimental values of lgP and pK_a. Further, the apparent extraction equilibrium constant K₁₁ was correlated with the above molecule structure parameters and the specific basicity of TOA based on the result of the second part of this paper, and 114 sets of experimental K₁₁ approached the correlated data well.