The solubility of diuron (3-(3,4-clichlorophenyl)-1, 1-dimethyl urea) and monuron (1-(4-chlorophenyl)-1, 1-dimethyl urea) in 49 and 43 different organic non-electrolyte solvents, respectively, have been calculated, It was found that Modified UNIFAC described well the solubilities both in polar solvents, like alcohols, ketones, esters and ethers and in nonpolar solvents like alkanes and aromatic hydrocarbons, UNIFAC and the mobile order theory supplement, each other well in calculating the solubilities, which means that one can choose the right model depending on the solvent one is using.