It has been demonstrated that azo dyes, the xenobiotics widely use in industries, can pose threats to public health. 3,3'-diaminobenzidine (DAB), as a benzidine analogue, is generated from reduction of azo dyes by intestinal or environmental microorganisms. The compound was applied at doses of 0 and 100 mg N/kg into two soils of contrasting textural properties belonging among Haplic Calsisols (Juzdan soil) and Calcaric Cambisols (Shervedan soil) and the effects on N mineralization kinetics were evaluated. Kinetic behavior of N mineralization in either the control or the DAB-treated soils consistently followed first-order models. In the early 7-10 days of the incubation period, net N mineralization was adversely influenced by DAB. After the early 7-10 days of incubation, the accumulation of inorganic N was greater in DAB-treated soils than those of control soils. This finding indicated that the degradation of DAB was started. Potentially mineralizable N in Haplic Calsisols and Calcaric Cambisols were 1.1 and 1.4 times greater than those of controls, respectively. Similarly, initial potential rates of N mineralization in the DAB-treated soils were 1.3 and 1.1 times greater than those of controls, respectively. The potentially mineralizable N and initial potential rates of N mineralization in both soils were significantly (LSD, P < 0.05) increased when soils were treated with DAB. About 95 and 82% of the initial DAB-N were mineralized to inorganic N after 60 days of aerobic incubation, respectively. Overall, DAB can be a potentially toxic xenobiotic for soil N mineralization shortly after application and the rate of its inhibition or stimulation is time-dependent.