Most of the semi-volatile organic compounds, which are environmentally important, are subject to long range atmospheric transport due to their chemical and physical properties. Their vapor pressure, solubility and indirectly Henry.s law constants are the most important parameters defining their fate during transport of these compounds. Especially in the air-water exchange process, Henry.s law constant plays an important role. Therefore accurate and direct measurement of the Henry.s law constant are required for the most of the compound present in the environment. In this study 17 organochlorine pesticides. Henry.s law constants were measured by a dynamic equilibration method at 5, 15, 20, 25 and 35 a1C in deionized water. The variation in H with temperature was expressed using the van.t Hoff type Gibbs-Helmhotz equation. Calculated enthalpy of phase change for each compound, which helps to describe how sensitive is the partitioning between air and water, within the range of the values reported in the literature. In Gibbs-Helmhotz plots, H values of a compound in saline water were always higher than the H values of that compound in deionized water. Therefore, it was concluded that in the saline water, the air-water partition of these chemicals is shifted to air phase.