With a liquid chromatographic column, methidathion transport behaviors in red soil and gray fluvo-aquic soil columns were studied, respectively. Three types of simulated soil solutions(0.01 mol x L(-1) CaCl2, 0.01 mol x L(-1) CaCl2 + 0.001 mol x L(-1) citric acid, and 0.01 mol x L(-1) CaCl2 + 0.001 mol x L(-1) malic acid) and two pore water velocities (11.46 and 22.92 cm x h(-1)) were applied. The breakthrough curves (BTCs) of Cl- and methidathion were obtained in these soil column experiments. With Software CXTFIT2.1, the local equilibrium assumption (LEA) model and nonequilibrium two-site model (TSM) were used to simulate the observed BTCs of methidathion. Consequently, the physical and hydrodynamic parameters from the fitting results were obtained. This study suggests that the TSM based on nonequilibrium theory can be used as a useful approach to better quantifying methidathion transport, which provide guides for predicating and controlling the methidathion fate in environment.