A new benzothiazole derivatives 4a-f were prepared by the reaction of2-cyanomethylbenzothiazole 1 with 2-hydroxy-5-(aryldiazenyl)benzaldehyde derivatives 2a-f under conventional method in ethanol containing few drops of triethylamine. The previous reaction was reinvestigated at room temperature using grindstone techniques in the presence of sodium hydroxide. The compounds 4a-f transformed into benzothiazole-bearing coumarin derivatives 5a-f by refluxing in dioxane with few drops of conc. hydrochloric acid. The structure of the newly synthesized compounds 4a-f and 5a-f was established by spectral data. The compounds 5a-f showed fluorescence properties as well as antimicrobial activity.