The fate of nicosulfuron in herbicide formulation (4% OD) under forced acidic and forced alkaline hydrolysis in HCl and NaOH as well as its photolysis in Egyptian clay soil samples was investigated in this study. The results indicated that nicosulfuron's shelf life and half-life were affected by an acidic medium with the herbicide half-life and shelf life being longer in HCl concentrations (0.01 N- 1.0 N). On the other hand, the shelf-life and half-life in 0.01N NaOH decreased to 1/5 of its values in 1.0 N NaOH.  The kinetics of nicosulfuron degradation was found to follow the first-order model which depended upon its initial concentration. Furthermore, nicosulfuron dissipation in Egyptian clay-loam soil (pH 8.59) was 27.67 days. The mechanism of nicosulfuron degradation in forced acidic and alkaline conditions as well as in soil photolysis was elucidated and was found to be caused by the initial cleave of the urea moiety. The major degradation products of nicosulfuron in the soil and the forced acidic degradation were identified to be 2-(aminosulfonyl)-N,N-dimethylnicotinamide and 2-amino-4,6-dimethoxypyrimidine in the forced acidic degradation, which were not evident in the forced alkaline condition. In the soil, a contraction reaction occurs, similar to what occurs in forced alkaline conditions.