Dimensionless Henry’s law constants of aromatic compounds in water were measured at various temperatures between 318.15-355.15 K using a headspace autosampler with a gas chromatography. This measuring system prevent, sample losses due to volatilization from equilibration, sampling, and chemical concentration analysis by a high precision headspace sampler and gives relatively accurate results. Dimensionless Henry’s law constant is calculated by thermodynamic relation and the mass balance with gas chromatographic peak area. Different equilibrium concentration in gas phase was made by using different gas-liquid volume ratio in sample vial. The temperature dependence of dimensionless Henry's law constant was correlated with the classical van’t Hoff equation as a function of temperature. The extrapolated data at 298.15 K from correlated equation were compared with available literature data in order to test this method.