The effects of dissolved organic matter (DOM), derived from compost, on the sorption of simazine by soils were studied using a batch equilibrium technique. Six soils with different organic carbon contents were investigated in this study. Simazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (K_d) or with DOM (K_d*) were obtained. Generally, the values of K_d*/K_d were initially increased and then decreased with raising DOM concentrations of 0-65 mg DOC·L in the soil-solution system form. Critical concentrations of DOM (DOM_np) were obtained, and the value of K_d* was equal to K_d. The presence of DOM with concentrations lower than DOM_np promoted simazine sorption on the soils (K_d* > K_d), whereas the presence of DOM with concentrations higher than DOM_np tended to inhibit the simazine sorption (K_d* < K_d). Interestingly, DOM_np for the tested soils was negatively correlated to the soil organic carbon content, and the maximum of K_d*/K_d (K_max) was correlated positively with the maximum of DOM sorption on the soil (X_max). Further investigations also showed that the presence of the hydrophobic fraction of DOM evidently promoted the simazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the simazine sorption.