Different mechanisms were suggested for nucleophilic aromatic substitution reactions so our study is made to find out the correct mechanism for the reaction, the rate determining step and the effect of hydrazine and hydroxide on the rate of the reaction. This thesis includes the study of the reactions of some 1-chloro-2-(trifluoromethyl)-4-nitro benzene derivatives: 2-chloro-5-nitrobenzotrifluoride (1), 4-chloro-3-nitrobenzotrifluoride (2), 2- chloro-3,5-dinitrobenzo-triflouride (7) and 4-chloro-3,5-dinitrobenzotriflouride (8) trivially known as chloronitrobenzotrifluorides and 2-chloro-3-trifluoromethylpyridine (3), 2-chloro-5- trifluoromethyl pyridine (13). The reactions of compounds (1), (2), (3) and (13) with hydrazine was done in pure DMSO and with sodium hydroxide in 10% aqueous DMSO. While the reactions of compounds (7) and (8) with hydrazine was done in 50% aqueous DMSO inorder to study the effect of extra nitro group on the rate constants and mechanism. The isolation and identification of the products for compounds (1), (2), (3) and (13) shows that the the reactions proceed with an additione limination process. As for the dinitro compounds the study at low ratio with hydrazine (1:2 molar ratio) at room temperature yields the hydrazino compounds with the addition-elimination process. On the other hand reflux with an excess hydrazine (1:30 molar ratio) gives other products 1-hydroxybenzotriazole derivatives. Its found that the change in the positions of the second nitro group increases both their rates of formation and disappearance.