The behavior of bifenox, a diphenyl ether herbicide, methyl 5-(2, 4-dichlorophenoxy)-2-nitrobenzoate, in soil was studied using two types of ¹⁴C-bifenox labeled at the nitrophenyl and dichlorophenyl rings, respectively. The evolution of ¹⁴CO₂ occurred in a passable amount in non-flooded (upland moisture condition) soil, but scarcely in flooded soil. Organic volatile metabolites were hardly detected under either moisture condition. In the early stage of degradation, fair amounts of the degradation products were adsorbed by soil with noncovalent bonds. Degradation patterns obtained under various degradation conditions, such as sterilization before or after pre-incubation, long term pre-incubation, addition of glucose, and different concentration of the chemical, indicate that the hydrolysis of the ester bond is due mainly to microbial reaction and the reduction of the nitro group to amino group is mainly to chemical (non-biological) reaction.