We studied adsorption state of water molecules in a porous coordination polymer (PCP) using infrared spectroscopy. We observed two absorbance peaks below 4% relative humidity (RH) that originate from OH stretch modes of adsorbed water molecules. Their peak frequencies and areas indicate that one of the OH is free, and the other is hydrogen bonded. We also found that Free-OH plays a role of water attraction above 4% RH, and discuss the water adsorption kinetics in detail.