The retention behavior of proteins was investigated by using hydrophobic interaction chromatography (HIC), comparing to the results obtained in reversed-phase chromatography (RPC) described in the previous paper. A SynChropak propyl column was employed with 0.05 M phosphate buffer (pH 7.0) containing sodium sulfate. Conformational changes were recognized by examining Z values as a function of sodium sulfate concentration over a range of temperature between 5 and 65$^{circ}C$. Z values did not change significantly at the range of the temperature showing the consistent ${Delta}H^{circ}$ and ${Delta}S^{circ}$ values. The sign and the magnitude of ${Delta}H^{circ}$ and ${Delta}S^{circ}$ of proteins in HIC were compared with those obtained in RPC. The signs of ${Delta}H^{circ}$ and ${Delta}S^{circ}$ of proteins in HIC were all positive, while those of proteins in RPC were all negative. These results suggested that the retention of proteins in HIC and in RPC were entropy-driven and enthalpy-driven process, respectively. From the two different investigations, it was concluded that the retention mechanism of RPC and HIC was based on the same fundamental principle in which separation is dependent on hydrophobicity, but the retention behavior of the proteins in HIC is clearly different from that observed in RPC.