The Schiff bases of (1a-e) isoniazid and 5-substituted- 2-furancarboxaldehydes on treatment with mercapto acetic acid yield, 4-thiazolidinone (2a-e) derivatives. These derivatives (2a-e) on Mannich base reaction with diphenyl amine and formaldehyde yielded the Mannich base products (3a-e). All the derivatives, (2a-e) and (3a-e) were characterized by elemental content and IR , NMR, LC-MS spectral data. All the derivatives have also been monitored for antibacterial activity.