In this project 2-mercaptobenzothiazole and its derivatives were prepared, and the biological activity has been measured in cooling fluids which has been taken from Chemical Central Research and Petrochemical Industries. Like the following: Part I: Organic synthesis: 2-Mercaptobenzothiazole [1] was prepared in easier fashion by treatment of aniline with carbon disulfide and sulfur in a steel autoclave. After that Sodium [2] and potassium [3] salts of 2- mercaptobenzothiazole were prepared through the reaction of 2- mercaptobenzothiazole with sodium and potassium hydroxide, respectively. Then Selective oxidation of the 2- mercaptobenzothiazole [1] into benzothiazole of disulfide [4] by using H2O2 under mild conditions was also demonstrated. The structures of the obtained products were proven by spectroscopic method (F.T.I.R). Part II: Biological activity : 1-The above synthesized compounds have been used as antimicrobial against the microorganisms which have been found in the cooling fluids of industrial purposes, by using media culture. The results showed that sodium and potassium 2-mercaptobenzothiazoles [2], [3] are comparatively highly active in killing bacteria. 2-The pH of the cooling fluid samples has been measured after the addition of salt media as well as the inhibitors (2-MBT, Na2-MBT, K2-MBT, BT-disulfide) the results of the pH measurement revealed that Na2-MBT, K2-MBT exhibit higher activity to inhibit the growth of bacteria compared with other synthesized compounds. 3-The Turbidity for such media and inhibitors has also been measured and the results indicated that Na2- MBT, K2-MBT have given low Turbidity compared to that of other synthesized compounds. The above results indicate the biological activity for the compounds Na2- MBT, K2-MBT are the best from the other synthesized compounds to inhibit the bacteria or the microorganisms that grow in the cooling fluids.