Herin we report the design, synthesis, full characterization and biological investigation of new 15-LOX/COX dual inhibitors based on 1,3-thiazolidin-4-one (15-lipoxygenase pharmacophore) and 1,3,4-thiadiazole (COX pharmacophore) scaffolds. This series of molecular modifications is an extension of a previously reported series to further explore the structural activity relationship. Compounds 3a, 4e, 4n, 4q, 7 and 8 capable of inhibiting 15-LOX at (2.74, 4.2, 3.41, 10.21, 3.71 and 3.36 μM, respectively) and COX-2 at (0.32, 0.28, 0.28, 0.1, 0.28 and 0.27 μM, respectively). The results revealed that binding to 15-LOX and COX is sensitive to the bulkiness of the substituents at the 5 positions. 15-LOX bind better with small substituents, while COXs bind better with bulky substituents. Compounds 3a, 4r and 4q showed comparable in vivo anti-inflammatory activity to the reference drug (celecoxib). The ulcer liability test showed no sign of ulceration which ensures the safe gastric profile. Docking study was performed to explore the possible mode of interaction of the new compounds with the active site of human 15-LOX and COX-2. This study discloses some structural features for binding to 15-LOX and COX, thus pave the way to design anti-inflammatory agents with balanced dual inhibition of these enzymes.