A series of new Schiff bases derived from benzothiazolone moiety were synthesized under thermal and ultrasound irradiation conditions, by reaction of 6-amino-benzothiazolone intermediates with various substituted 2- hydroxybenzaldehydes. The chemical structures of the prepared compounds 5a-5h were characterized by their melting point, spectral and analytical data. The newly synthesized compounds were in good agreement with the proposed structures. Ultrasound irradiations gave a lower reaction time to offer products 5a-5h in higher yields than those obtained by the conventional method where their yields increased from 67-87% to 91-98%. All the compounds were screened for in vitro antioxidant activity. The free radical scavenging activities have been determined by measuring their interaction with the stable free radical 2,2-diphenyl-2-picrylhydrazylhydrate. Result indicated that the 6-(5-Bromo-2-hydroxybenzylideneamino)benzo[d]thiazol-2(3H)-one (5e) showed the most favorable antioxidant activity exhibiting IC50 of 32.55 μM.