Several kinds of esters are widely used in synthetic lubricants. The evaluation of their influence on the environment is a matter of considerable interest. This paper studies the ultimate aerobic biodegradation of several phthalates, such as dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), di-n-octyl phthalate (DOP) and di(2-ethylhexyl) phthalate (DEHP), and their degrading kinetics by quantitative assessment of the carbon dioxide produced. The production of CO 2 was chosen as the evaluation parameter to determine the biodegradability of phthalates in aqueous solution. A kinetic model was established to describe the biodegradation process of phthalates. The results indicated that biodegradation of phthalates followed the first-order kinetic equation; the rate constant (k b ) of biodegradation decreased as the carbon number of the alkyl chain increased, and linear phthalates had better biodegradability than branch phthalate. When the initial concentration was over 200 mg/L, a lag phase was evident during the degradation of phthalates, which was prolonged with increased carbon number in the alkyl chain. Easily biodegradable organics, such as glucose, had a favorable effect on the aerobic biodegradation of phthalates.