Environmental organic chemicals disappear by means of transport and mixing phenomena and alterations of the structure of a compound. The transport phenomena can be represented by partition coefficient. In this work, the air/water partition coefficient(K_aw) was measured by using our own modified EPICS(equilibrium partitioning in closed system) method. The accuracy and reproducibility of this method were reliable since measured data were agreed well with the literature values within 1% average deviation for n-alkanes. The K_aw and Henry's law constants for n-alkenes, aromatic and chlorinated compounds were measured. The relationships between K_aw and molar volume, vapor pressure and water solubility were also analysed. The K_aw was linearly proportional to molar volume and inversely proportional to vapor pressure and water solubility except chlorinated benzene compounds. The chlorinated benzene compounds didn't show the consistent tendency for molar volume, vapor pressure and water solubility. It may be caused from the difference of intermolecular force. The K_aw was changed by difference of molecular structure. The weaker the bond energy of chemicals, the larger the K_aw of chemicals.