N-Acetyl-1-phenylalanyl-1-phenylalanine methyl ester (APhPhMe), N-acetyl-l-phenylalanine methyl ester (APhMe) and N-acetyl-1-phenylalanyl-1-alanine methyl ester (APhAlMe) were used as model compounds to investigate a protein denaturation under various temperatures and pressures. Overall, the solubility of APhPhMe in water increased with increasing pressure and that of APhMe decreased. However, the solubility of APhAlMe was nearly same. The values of volume change of APhPhMe were -0.9, -1.47, -1.09, -1.52 ml/mole at 20, 30, 40 and 50$^{circ}C$, respectively, and those of APhMe were +6.0, +7.0, +7.5 ml/mole at 20, 30 and 40$^{circ}C$, respectively. But those of APhAlMe were nearly zero at the measured temperature. The experimental result seems to be explained by the hydrophobic interaction and hydrogen bond of peptide bonds. In the compounds which have only peptide bonds and which have both a pretty large hydrophobic group and a peptide bond in the molecules, the hydrogen bond between peptide bonds is more dominant than the hydrophobic interaction. However, when the number of peptide bond and hydrophobic group increase simultaneously, the hydrophobic interaction seems to be more dominant.